Quick answer y = 4x + 9
Argument
The first thing you are given is the slope. The original equation has a 4 in front of the x and 1 one in front of the y. Those two conditions allow you to say that the slope of the line is whatever number is the slope of the line. In this case slope of the new line is 4.
So far what you have is
y = 4x + b
The point (0,9) gives you b.
9 = 4*0 + b
b = 9
Complete Line
y = 4x + 9