5) first find the gradient using the formula:
y2-y1/x2-x1 (you have to use 2 sets of coordinates on the line)
im using the coordinates (20,40) and (35,50)
50-40/35-20
=10/15
gradient = 2/3
y=2/3x+c
subsitute a set of coordinates
im using (20,40)
40 = 2/3 (20) + c -> (c is the y intercept)
40 = 40/3 + c
c = 40-40/3
c = 80/3
y = 2/3x + 80/3
6) repeat
find the gradient, im using the points (40,20) and (30,50)
50-20/30-40
30/-10
gradient = -3
to find the y intercept, subsitute a pair of coordinates into
y = -3x + c
im using the coordinates (40,20)
20 = -3(40) + c
20 = c - 120
c = 20 + 120
c = 140
y = -3x + 140