The base fee of $15.99 is going to have to be paid, whether any miles are put on the truck or not. If the number of miles driven is our unknown, if we rent the truck for the base fee of $15.99 and drive it 0 miles, we still have to pay the $15.99. If we do drive it and we have to pay .92 a mile, the expression for that is .92x, where x is the number of miles driven (it is also the variable we are solving for!). The expression for this total cost is .92x + 15.99, and since we paid a total of $194.47, we set our cost equation equal to that number and solve for x:
