Determine the optimal number of hours to use machines a and b to excavate and grade a cul-de-sac at minimum cost. solve using graphical method. given a construction site has machines that simultaneously excavate and grade machine a grades: ga = 18.9 unit h-1 and excavates: ea = 15.5 unit h-1 the cost to operate machine a is: ca = 101 $ h-1 machine b grades: gb = 10.2 unit h-1 and excavates: eb = 23.2 unit h-1 the cost to operate machine b is: cb = 1.10e2 $ h-1 each machine can be assigned to the cul-de-sac for no more than 10 hours. amount of grading: g = 100 unit amount of excavating: e = 150 unit "units" here are a measure of volume