Ineed the equation of the line in the graph

First of all, we know that it's a linear equation, which means it'll have to be y=mx+b.

Identify your points.
(0, 0) and (5, 4).

Now find the slope by doing 
m = (y₂ - y₁)/(x₂ - x₁)
m = (4 - 0)/(5 - 0)
m = 4/5
So the slope is 4/5 or 0.8.

Now set the equation up. You have a point and the slope, so use the point-slope equation.
y - y₁ = m(x - x₁)
y - 4 = 4/5(x - 5)
y - 4 = 4/5x - 4
y = 4/5x

So the equation of the line is y=4/5x.