The gas tank of your car is 40% full. There are 8 gallons of gas in the tank. What is the capacity of the gas tank?

Percentage by which the gas tank of the car is full = 40%

Amount of gas in the gas tank = 8 gallons

Let us assume the capacity of the gas tank = x gallons

Then

40% * x = 8

(40/100) * x = 8

4x/10 = 8

4x = 8 * 10

4x = 80

x = 80/4

= 20 gallons

So the total capacity of the gas tank of the car is 20 gallons. I hope the procedure is clear to you.