[instarx]

Actually, because the multiplication has to be done before the addition I'd write it this way:

(($4.39 * 1 gallon) + ($3.99 *10.25 gallons)) / total gallons

therefore

(4.39 + 40.89) / 11.25 = $4.025

The Excel equation would be

=((4.39*1)+(3.99*10.25))/(1+10.25)

Note the double parentheses in the numerator.