Can someone help me with these math problems?

1. The circumference of a circle is 31.4 inches. Find the radius of the circle in inches. Round to the nearest whole number. Justify your answer.

2. The radius of a circle is 7 centimeters.
Find the circumference of the circle, in centimeters. Round your answer to the nearest hundredth. Justify your answer.

3. Anna cuts two identical circles from a rectangular piece of black poster board as shown. (7.G.4)
What is the area of the leftover black poster board? Use 3.14 for π. Show your reasoning.

4. The circumference of the circle is approximately 100.48 centimeters. The shaded region is of the whole circle. Find the area of the shaded region in square cm. Round your answer to the nearest hundredth. Justify your answer.