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!
