The circumference of a circular plot of land is increased by 10%. What is the best estimate of the total percentage that the area of the plot increased?

(1) 10% (3) 25%

(2) 21% (4) 31%

The answer is 21%. I have no idea how to even start this question.

I know that A = pi(r^2) and C = pi(d)

This question makes no sense to me.