One way trip distance = 640 miles
Round trip distance = 640 x 2 = 1280 miles
The mileage of Robin's car = 30 miles per gallon
To cover 1280 miles, Robin will require:
[tex]\frac{1280}{30}=42\frac{2}{3}\text{gallons}[/tex]Since each gallon costs $3.71, 42 and 2/3rd gallon will cost:
[tex]42\frac{2}{3}\times3.71=\$158.29[/tex]The total cost of the trip - $158.29
Answer$158.29