Sorry that i posted at this late hour..... Just came back from YOG....
1) If (a,b) lies at y=mx+c, then b=m(a)+c
2) Gradient is = rise divided by run = change in y coordinate divided by change in the x coordinate.
THE ORDER IS IMPORTANT
3) y - 1x +c (Coordinates 1,5 and -3,1)
To find c, you have to find x. It can go two ways;
Either you substitute the coordinates (1,5) and get
c = 4#
1 = 1(-3)+c
.: c = 4
4) To satisfy an equation means to balance both sides of an equation.