Answer:

Explanation:
Let's start off by trying to find the slope/gradient (commonly denoted as
) of this function

This means we divide the change in y over the change in x
Let's pick, for example, x = 3 (who's corresponding y is 150) and x = 4 (who's corresponding y is 200)

Now we have this:

Let's plug in a random value of x and y from this function in order to find b. I'll pick x = 2:

Since b is 0, we don't have to write it on our equation, meaning that our final equation is just

To verify this, let's say we didn't know the value of y when x is equal to 4 and all we had was that equation:

Just like it is on the graph :)
Good luck!