I believe it would be y = mx + b
So we have our slope, which is m. And we have a coordinate point (both x and y) (0,4) So now plug them all into the equation.
4 = 3.5(0) + b
4 = 0 + b
4 = b. Your answer for B would be 4.
So now your entire equation is y = 3.5x + 4
Hope this helped!
-TTL