Which graph represents the function of 9x^2 - 36 over 3x + 6

If this is what you mean,

Notice clearly, we can factor 9x^2-36 out, same with 3x+6

From x^2-4, use the Difference of Two Squares,

To find the x-intercept, y or f(x) = 0

Now we know the x-intercept. To find the y-intercept, x = 0 therefore,

So point or dot at x = 2 and y = -6 then draw the line. It should be like the graph shown below (Image.)

this is answer of 144 cubic meters