Question 436742
y = mx + b ==> 5 = -3m + b, and 

4 = 5m + b

Multiply 5 = -3m + b by 5, to get 25 = -15m + 5b
Multiply 4 = 5m + b by 3 to get 12 = 15m + 3b
Add:

37 = 8b ==> b = 37/8, the y-intercept.