Question 508298
First, you have to determine the equation for the line that has an x-intercept of 7 and a y-intercept of -56. 
This information defines two points:
(7,0) and (0,-56)
To define the line, you need to determine the slope, m.
m = (0-(-56)) / (7-0)
m = 56/7
m = 8
.
So the line's equation is:
.
y = 8x -56
.
A line perpendicular to it will have slope = -1/8. That defines
.
y = -1/8 + b
.
You can use the required point (-3,7) to find 'b'
.
7 = -1/8(-3) +b
7 = 3/8 + b
b = 6 5/8
.
y = -1/8*x + 6 5/8
or
y = -1/8*x + 53/8
.
In the following graph, the red line is y = 8x-56, the green line is y = -1/8x + 53/8
.
{{{graph(500,500,-10,10,-10,10,8*x -56, -1/8*x+6+5/8)}}}