The line should go through the points 50 and 0−8 which must therefore satisfy the equation of the line y=kx+m, i.e.
0=k5+m
From the other equation, we get m=−8 and substituting this into the first equation gives
0=5k−8 k=85
The gradient of the line is 85.
5
0
0−8 
5+m
k=8
55
