Does anyone know the answer to this

I did this on paper at first because I wanted to see if it was correct, and I think it is, but I'll double check after I have posted this just incase. So, you need to solve for r to find the radius of the large circle, and you can do this by forming an equation:
(π × r²) + (π × 2r²) = 80π
2π × 3r² = 80π
÷ 2π
3r² = 40
÷ 3
r² = 13.33
√
r = 3.65

Because the radius of the larger circle is 2r, you need to multiply r by 2 to get 7.303 as your answer. I hope this helps!