 Okay, so in this example we're taking fuel economy analysis into consideration and what we're doing is converting from one set of units of fuel economy to another set of units. So the one would be in kilometers per liter, like maybe in Europe or something, and you convert that to miles per gallon like you would use in the United States. So you have this Toyota Prius and it gets 21 kilometers per liter and you want to figure out well how many miles per gallon is that. In order to do that you're going to of course have to convert the kilometers to miles, they're both distance units so you can do that with conversion factors and of course the liters into gallons and since those are both volumes you can do that with conversion factors. So you just need to find the right ones and luckily enough the problem gives them to you. So you've got the one liter equals 0.264 gallons conversion factor so you use that first to get rid of liters, convert the volume units to gallons and then of course you want to convert your distance units to miles so you just use the other conversion factor putting kilometers on the bottom, canceling them out and we get miles per gallon. And we have to go back to the given numbers to see what significant figures we want and since there's two sig figs in the given numbers at 21 kilometers per liter you're going to put two sig figs in your answer. So your answer is going to be 49 miles per gallon, hopefully this makes sense.