4/7 is the answer.
I cant reall explain becuase it will take forever xD
A. $40, because you would do 1,000 × 1.04 = $1,040, and then subtract the original $1,000.
b. $81.60, because 1,000 × 1.04² = 1,081.6
c. $480.24, because 1,000 × 1.04^10 = 1,480.24.
I have used the formula for compound interest presuming you were aware of it, but I will be happy to explain what I did if you want :).
I hope this helps!

You need to work inside out.

simplifies to

.
Now you need to cube that.

Therefore the solution is

.
Some numbers you must know automatically know, so my suggestion is either search up the number or if you divided keep it with the division as a fraction.