Help please :). I hate trigonometry

What percent of the circle below is shaded?

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

Prove that the value of the expression 7^8–7^7+7^6 is divisible by 43.