I need help. How can you find the value of K but please don't solve it, just tell me how to work it out.

Example:
Given f(x) and g(x) = k⋅f(x), use the graph to determine the value of k.

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