Question 678210
Step 1: Find the radius of each circle.

{{{2*pi*r[1] = 30*pi}}}                  

{{{r[1] = 15}}}                                 

{{{2*pi*r[2] = 40*pi}}}

{{{r[2] = 20}}}

Step 2: Find the areas of the 2 circles.

{{{A[1] = pi*r[1]^2 = 225*pi}}}

{{{A[2] = pi*r[2]^2 = 400*pi}}}

Step 3: Subtract the smaller circle area from the bigger circle area.

{{{A[ring] = A[2] - A[1] = 175*pi}}}