If the total volume of the box is 24 cm³ and the volume of each cube is 1 cm³then that means that 24 total cubes can fit perfectly inside the box. Since there can only be two layers of cubes then we simply need to divide the total amount of cubes that will fit in the box by 2 to find the number of cubes in each layer...
24 / 2 = 12 cubes
Finally, we can see that each layer within the box will contain 12 cubes
You wouls do 125 times 135% and that would be 168.75 then you would do 125 add 168.75 which would equal 293.75 then you would do 293.75 times 7.5% which equals 22.03 then you would do 22.03 add 293.75 and the answer would be 315.78