$12.$ Edmund Stench loves punk rock video tapes. He has no income and therefore has to accept garbage in his backyard in return for money. Each video tape cost $$2$ and each sack of garbage that he accepts brings him $$1.$ His utility function is given by U$($c$,$ g$)=$ min$\{2$c$,20$ g$\},$ where c is the number of video tapes and g is the number of sacks of garbage that he gets per month. Each month he can afford to buy how many video tapes.