3t + 2b = 95
t + b = 40
t + b - b = 40 - b
t = 40-b Substitute this in the formula marked
3(40-b) + 2b = 95
120-3b+2b=95
120-b= 95
120-120-b=95-120
-b= -25
-1b/-1=-25/-1
b= 25
Plug b= 25 into t + b = 40
t + 25 =40
t + 25 -25 = 40-25
t = 15
15 tricycles and 25 bicycles