firstly , we must find the gradient.
gradient, m = y2 - y1 / x2 - x1
m = 7 - (-1) / 4 - 3
m = 8
a straight line is y=mx+c
thus, we have to find the c which is y-int by subs one of the coordinate to the equation.
y=mx + c
7=8(4) + c
c = -25
thus the equation is y = 8x - 25