12. A machine shop manufactures two types of screws: sheet metal screws, m, and wood screws, to, using three different machines. Machine I can make a sheet metal screw in 20 sec and a wood screw in 5 sec. Machine II can make a sheet metal screw in 15 sec and a wood screw in 15 sec, while Machine III takes 5 sec and 20 sec for each screw, respectively. Each machine can operate for at most 3 hours per day. If sheet metal screws sell for 10 cents and wood screws sell for 12 cents, how many of each type of screw should be made in order to maximize the shop's revenue? If this problem were formulated as a linear programming problem, what would be the corre- sponding units of the necessary inequality 20m + 510 S 10, 800? (a) Minutes (b) Number of screws (0) Cents ((1) Hours ) (e Seconds