The equation to represent the total monthly cost, C, for maintaining a house and for h hours of extra work is C = 25 + 15h. This equation states that the total cost is equal to the fixed monthly fee of $25 plus $15 multiplied by the number of hours of extra work, h. For example, if Doretta is hired to do 5 extra hours of work, the total cost would be C = 25 + 15(5) = $100.