Help please if you can

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

If x is 6, then 7x= a. 13 b. 42 c. 42x d. 76

Consider a cube that has sides of length l. now consider putting the largest sphere you can inside this cube without any point on the sphere lying outside of the cube. the volume ratio -volume of the sphere/ volume of the cube is 1. 5.2 × 10−1 2. 3.8 × 10−1 3. 1.9 4. 2.5 × 10−1 5. 3.8