y = 20x
The graph passes through the origin , hence is of form
y = mx ( m is the slope )
to calculate m use the gradient formula
m = (y₂ - y₁ ) / (x₂ - x₁ )
with (x₁, y₁) = (2, 40) and (x₂, y₂) = (4, 80) ← 2 points on the graph
m = [tex]\frac{80-40}{4-2}[/tex] = [tex]\frac{40}{2}[/tex] = 20
y = 20x
