 Let's look at how we calculate the volume of an object. The volume is measured as the capacity of a three-dimensional object. And the volume is always measured in cubic meters, in meter cubed. We can calculate the volume for a cube, a prism, or a cylinder. A cube is like a box, which has four sides that are equal. A prism, it's also like a box where it has two sides that are equal. All sides are equal on the cube. And a prism, two sides are equal. And a cylinder is like a can or a tube. We can calculate the volume because we calculate what goes inside. If we have to fill it up, how much can we fill it up with? That's the volume. That's the formulas for each. To calculate the volume for a cube, we use L squared. To calculate the volume for a prism, we use the length times the breadth times the height. To calculate the volume of a cylinder, we use the circle, which has a radius. So we use the area of a circle formula, pi R squared, multiplied by the height. Before we look at an example, we need to also understand that when we work with volume, we need to do some conversions from meter cube or centimeter cube to liters because volume is always calculated or the units for volumes are always in liters. So let's look at some of this. A one liter is equivalent to a thousand centimeter cube. And also a one liter is equivalent to a thousand milliliters. Therefore, it means one milliliter is equivalent to one centimeter cube. And also one kilo liter is equivalent to one meter cube. You need to understand all these conversions from a kilometer to meter to liters to centimeter to milliliters. All this, if you're doing QMI or BNU, they are in your module. You just need to understand and know how to do those conversions. Okay, enough with this. Let's look at an example. A circular water reservoir has a maximum capacity of a 10,000 kilometers. Its diameter is 80 meters. How deep is your reservoir? Probably the how deep they wanted the answer in meters. I'm just making that assumption because we want to calculate the height. We want to calculate the height. How deep? Therefore, it means they also gave us the diameter. They said the diameter is 80 meters. They told us the blue shaded area, which is our volume, is 10,000 kilometers. Now we have two units that are different. Kililiters and meters. We need to find how deep, which is in meters. It means we need to convert our kililiters to meters or meter cubes. And before we do that, the formula to calculate the cylinder is V is equals to high R squared times height. What is the diameter? And we know the diameter is 8. Therefore, our radius is equals to 30 divided by 2, which is 15. And we can substitute into the formula. Our volume is 10,000 kilometers. And we know from previous that one kilometer is equivalent to one centimeter cube. So therefore, it means our 10,000 kilometers, 10,000 kilometers, they are equivalent to 10,000 meters. Therefore, it means now we can substitute into the formula because then we will be working with meters. So 10,000 meters cube is equals to pi, which is the diameter is 15 meters times height. We don't know what the height is. Now we can take the 15 meters square, which is pi is 225 meters squared times height. Now we can divide both sides. So we divide the side by 225 meter cube times pi and also decide by 225 meter cube times pi. Pi times 225 meter cube is equivalent to 707. So this is 707.1429 meter cube times height. Don't repeat. So this will be meter cube. And we can divide the side by 707.1429 meter squared. What you do on that side, you must do on this side 707.1429 meter squared. And when we do that, this cancel out with that and we are left with H on the other side. And on this side, when we divide the meter squared and meter cube, we left with meters and 704, it goes how many times into 10,000. 707 goes 14,14 meters. And that is how deep is the rest of all.