Use y = mx + b
plug in what you are given
m = slope so that is 2
y = 2x + b
then plug in the x and y coordinates to solve for b
5 = 2(2) + b
5 = 4 + b
subtract 4 from both sides
1 = b
The equation: y = 2x + 1
plug in the x- coordinate of the second point (that has the missing y-coordinate)
y = 2(4) + 1
Solve
y = 8 + 1
y = 9
The missing y-coordinate of the second point is 9 so the coordinate point looks like (4, 9).
Hope this helps :)