Since the surface area of a cube is 6 times the square of the side length of the cube, then that means the surface area of a cube that has a side length of 5 has a surface area of 6 x 5 x 5. 5 times 5 = 25, and 25 x 6 = 150
The next term in the sequence can be determined by subtracting 1.5 from 3.9 which is 2.4 and then you test it and say 3.9 plus 2.4 is 6.3 then plus 2.4 is 8.7 then the next term would be 11.11