30 gallons of fuel costing 3.35 per gallon must be mixed.
Explanation
Suppose, [tex]x[/tex] gallons of fuel costing 3.35 per gallon must be mixed with 20 gallons of another fuel costing 3.85 per gallon.
So, the total amount of the mixture [tex]=(x+20) gallons[/tex] and the cost of the mixture is 3.55 per gallon.
So, the equation will be....
[tex]3.35x+(3.85*20)=3.55(x+20)\\ \\ 3.35x+77=3.55x+71\\ \\ 3.35x-3.55x=71-77\\ \\ -0.20x=-6\\ \\ x= \frac{-6}{-0.20}=30[/tex]
So, 30 gallons of fuel costing 3.35 per gallon must be mixed.
