Let b represent the number of new bikes and u represent the number of used bikes. We were told that the motorcycle shop maintains an inventory of five times as many new bikes as used bikes. This means that
b = 5u
If there are 90 new bikes, it means that b = 90. Substituting b = 90 into the equation, it means that
90 = 5u
u = 90/5
u = 18
There are 18 used bikes in stock
