Iknow there will be a difference between the real answer and the estimated answer but the problem is i do not know how to someone pls ? thks a lot and the answer is correct right?

Ben frank is an electrician who installs lighting fixtures. he charges (in dollars) his clients 15h+40f15h+40f where hh is the number of hours worked and ff is the number of fixtures installed. how much does ben frank charge when he works 77 hours and installs 99 fixtures?