At a bicycle shop, a bicycle costs $49 and a tricycle costs $27. an after-school club buys bicycles and tricycles with a total of 39 wheels. the club buys 2 more bicycles than tricycles. a. how many bicycles does the club buy?

Let b for the number of bicycles, and t for the number of tricycles.
2b+3t=39  ( a bicycle has 2 wheels and a tricycle has 3 wheels)
b=t+2  =>t=b-2

substitute b for t: 2b+3(b-2)=39
2b+3b-6=39
5b=45
b=9
the club buys 9 bicycles and 7 tricycles.