 Hello and welcome to the session. The question says, the diameter of a metallic ball is 4.2 centimeters. What is the mass of the ball if the density of the metal is 8.9 grams per centimeter cube? So, first let us learn the formula to calculate the volume of a sphere. This is equal to 4 upon 3 pi r cube, where r is the radius of the sphere. This is the first formula and second formula to calculate the mass is equal to density into volume. So, here we have to find the mass of the ball and we are given the density. So, first we have to find the volume. So, volume we will find with the help of the first formula. So, with the help of these two formulas we are going to solve the above problems. So, this is our key idea. Let us now begin with the solution. Now, here we are given the diameter of the metallic ball is equal to 4.2 centimeters. Therefore, its radius is equal to diameter upon 2 that is 4.2 centimeters upon 2 is equal to 2.1 centimeters. Now, let us find the volume to find the mass of the ball. So, volume is given by 4 upon 3 pi r cube. So, we have 4 upon 3 into 22 upon 7 into r is 2.1 into 2.1 into 2.1 centimeters cube. This is further equal to 7 into 0.3 is 2.1 and 3 into 0.1 is 0.3. So, we have 4 into 22 into 0.1 into 2.1 into 2.1 centimeters cube. And this is further equal to 38.808 centimeters cube. So, this is the volume of the ball. Now, we have to find the mass of the ball and by a key idea we know that mass of the ball is given by the product of the density of the material of which the ball is made into the volume of the ball and this is equal to density is given to us as 8.9 grams per centimeters cube into volume is 38.808 centimeters cube. This one simply find comes equal to 345.39 grams approximately. Hence, our answer is the mass of the ball having diameter 4.2 centimeters is 345.39 grams approximately. So, this completes the session. Bye and take care.