How do i find the center of gravity of this figure?

https://i.stack.imgur.com/68z2R.png
How do i find the center of gravity of this figure? M = 14a N= 6a. I know I have to find the area of both circles then big one - small one.(that's what we did In class),but didn't understand what to do after. thanks in advance :)
There is a simpler way : take the center of gravity of the first disk weighted by its positive area $\pi 49 a^2$ and the second one weighted by its negative weight $-\pi 9 a^2$, all being divided by the algebraic sum $\pi 49 a^2-\pi 9 a^2=\pi 40 a^2$.