Algebra question

Question

A family has two cars during one particular week the first car consume 30 gallons of gas in the second consume 25 gallons of gas and the two cars and drove a combined total of 1675 miles in the sum of their fuel efficiency’s was 60 miles per gallon what were the fuels efficiencies of each of their cars that week?

Answer 1

let r and R be the fuel efficiencies

30r+25R=1675

r+R=60

R=60-r

substitute

30r+25(60-r)=1675

30r+1500-25r=1675

5r+1500=1675

5r=175

r=35 mpg

35+R=60

R=60-35

R=25 mpg