Radio station KMA is increasing its radio listening radius from 40 miles to 50 miles. How many additional square miles of listening area, to the nearest tenth, will the radio station gain?

Question

I thought it was 10 miles.But it says round.So im a little confused.If you could Help.I would be very happy.

the area of a circle is pi * r^2
if the first radius is 40 miles, then the area is pi*1600. the second radius is 50 miles, so the area is pi*2500. 2500(pi)-1600(pi)= 900(pi) additional sq miles of area. and then you multiply 900 and pi to get the answer.