Lakota brought 6 new compact disk and 2 used compact disk for $127.92. At the same prices Mackenzie brought 3 new compact disk and 8 used compact disk for $133.89. Find the cost of buying a single used compact disk

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?