Question 765366
Bicycles = x
Tricycles = y
x + y = 37....1
2x + 3y = 90...2
Multiply (1) by 3
3x + 3y = 111...3
2x + 3y = 90....2
Subtract (2) from (3)
x       = 21
Substitute x = 21 in (1)
x + y = 37
21 + y = 37
     y + 37 - 21
     y = 16
So, there are 21 bicycles and 
16 tricycles.
Hope this helps.
:-)