Bot for each birdhouse, Cooper uses 7 pieces of wood and some nails. He uses 3 times the number of nails as pieces of wood for each birdhouse. He sells each birdhouse for $12. If Cooper has lots of wood, but only 89 nails, how much money can he make selling birdhouses?
For each birdhouse, Cooper uses 7 pieces of wood and 3 times the number of nails, so he uses 7 * 3 = <<7*3=21>>21 nails.
He has 89 nails, so he can make 89 / 21 = <<89/21=4>>4 birdhouses.
If he sells each birdhouse for $12, he can make 12 * 4 = $<<12*4=48>>48. Answer: \boxed{48}.