Not sure how to setup this word problem

Question

A family has two cars. The first car has a fuel efficiency of
40
miles per gallon of gas and the second has a fuel efficiency of
25
miles per gallon of gas. During one particular week, the two cars went a combined total of
1225
miles, for a total gas consumption of
40
gallons. How many gallons were consumed by each of the two cars that week?

Answer 1

let x=# of gallons used by the 40 mpg car

let 40-x=# of gallons used by the 25 mpg car

40*x+25*(40-x)=1225

40x+1000-25x=1225

15x+1000=1225

15x=1225-1000

15x=225

x=225/15

x=15 gallons used by the 40 mpg car

40-x=40-15=25 gallons used by the 25 mpg car