There are 74 tricycles and bicycles in a shop.

There are 87 more wheels on the tricycles than on the bicycles.
How many bicycles are there?

b+t = 74

3 t - 2 b = 87

3(74-b) -2b = 87

222 - 3 b - 2b = 87

5 b = 135

b = 27