please help please

Question

How many gallons of fuel costing $1.15 per gallon must be mixed with 20 gallons of a fuel costing $0.85 per gallon to obtain a mixture costing $1 per gallon?

Answer 1

Let x = number of gallons of $1.15/gallon fuel

1.15x + 0.85(20) = 1(x + 20)

1.15x + 17 = x + 20

0.15x = 3

x = 20 gal