Question

Does anyone know the answer for this?

Answer 1

8 cm

Explanation:

The area of the shaded portion is:

`a = \pi * (( {r1)}^(2) - {(r2}^(2)))`

A=39π cm^2

r1 is the radius of the large circle

r2=5 cm

So,

`39\pi = \pi * (( {r1)}^(2) - {5}^(2) ) \\ r1 = 8 \: cm`