Respuesta :

Answer:

15

Step-by-step explanation:

The formula for factoring a sum of cubes is:

[tex]a^3+b^3=(a+b)(a^2-ab+b^2)[/tex]

We have a=3f and b=5g here.

So a*b in this case is 3f*5g=15fg.

The ? is 15.