The total cost of a model plane and a model boat is $9. The total cost of 3 model planes and 2 model boats is $22. What is the cost of a model plane? What is the cost of a model boat?
p + b = 9 ... so .... b = 9 - p
3 p + 2 b = 22
3 p + 2(9-p) = 22
p + 18 = 22
p = 4
b = 9-4 = 5