What is X? Please show me how to do this!

Acircle has a circumference of 28.36 units what is the diameter of the circle

Which of the following three dimensional figures has a circle as it’s base

You have a square piece of cardboard that measures 14 inches on each side. to build a box, you cut congruent squares out of each corner of the cardboard. use the picture to find the area of the cardboard you were used to build the box