Can someone explain to me how to solve these?

1.So, for the first problem, the Area Formula is A=pi*r^2
You would plug in what you know, the radius. 
Therefore, it would be A=pi*13^2 (13*13=169)
A=pi*169
A=530.929 square units.
2. This is 1/4 of a circle. the radius is still shown as 28.
So, the new formula would be A=pi*r^2 div. by 4
A=pi*28^2 div. by 4
A=pi*784 div. by 4
A=2463.009/4
A=615.752 square units.

50.2450.24 in squared