Solving a value

Question

A family has two cars. The first car has a fuel efficiency of 30 miles per gallon of gas and the second has a fuel efficiency of 20 miles per gallon of gas. During one particular week, the two cars went a combined total of 1300 miles, for a total gas consumption of 50 gallons. How many gallons were consumed by each of the two cars that week?

Answer 1

Let x = number of gallons used by the first car.

Then 50 - x = number of gallons used by the second car.

30x + 20(50 - x) = 1300

Solve for x.