What's the area of the shaded region?

Do you remember how to find the area of a circle ?

Big Fat Hint:  The area of a circle is  (pi) x (its radius)² .

Can you find the area of the big circle ... the one with radius = 18 m ?
Do that.  The whole big circle, just as if there was nothing inside it, and
no shaded region.
I'll wait.

Now, can you find the area of the small circle ... the one with radius = 12 m ?
Do that.
I'll wait.

The area of the shaded region is just

         (the area of the big circle) minus (the area of the small circle) !

I got 180 pi or roughly 565.2 m².  I could be wrong.  You should check it.

The answer would be 13.5 minutes.