Eva earns $72 washing 6 cars. At this rate, how many cars did Eva wash to earn $132?

Eva earns $72 washing 6 cars. At this rate, how many cars did Eva wash to earn $132?

Set up a proportion of money to cars washed where c is the number of cars washed for $132 in earnings:
72/6 = 132/c

Type this proportion into our calculator, we get:
c = 11