any help would be greatly appreciated thankyou
Yep, integrate twice here, look at this example, could be helpful.
( 843, #35) The average value of a function f(x,y) over a rectangle R
The "average value" of f(x,y) over $\displaystyle a\le x\le b$, $\displaystyle c\le y\le d$ is
$\displaystyle \frac{\int_{x=a}^b\int_{y= c}^d f(x,y)dy dx}{(b-a)(d-c)}$.
That is, it is the integral of the function over the region divided by the area of that region.