Answer:
The gradient is 3/7 make y the subject. Then put the coordinates in the equation.
Step-by-step explanation:
(a)

= 400
(b)


(c) Only the positive solution makes sense because you cannot have a negative side length.
(d) Since one side of the painting is 20 inches, all four sides together will be 20*4 = 80 inches
5=1/5x-3
+3 +3
8=1/5x
8•5 1/5x•5
40=x