How do you factor the coefficient of 3/8d+3/4?

Ihave trouble finding the nth term of a linear sequence

The square root of 9x plus 7 plus the square rot of 2x equall to 7

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