@Browbffangel13 has the right idea when finding the perpendicular slope to be m = -4, but the point (1,5) is not the y intercept. The y intercept only happens when x = 0.
y = mx+b
y = -4*x + b .... plug in the perpendicular slope m = -4
5 = -4*1 + b ... plug in the point (x,y) = (1,5)
5 = -4 + b
5+4 = -4+b+4 .... add 4 to both sides
9 = b
b = 9 .... which is the y intercept
Therefore, the answer is y = -4x+9