We know that
DF is the diameter of the circle
so
radius r=DF/2----->20/2-----> r=10 in
area of the circle=pi*r²------> pi*10²-----> 100*pi in²-----> 314 in²
the answer is
100*pi in² or 314 in²
B I’m not 100% sure but I think
By "density" I assume you mean "probability density function". For this to be the case for

, we require

Since

you have

which means
Simple the answer is c 100% positive