Question 957509
Treat each term in the binomial as a separate variable.  The pattern for the coefficients would go like, 1, 3, 3, 1, in accordance to what you would find if you were to do the cubing with a simple model such as  {{{(a+b)^3}}}, or referring to the Binomial Theorem.


{{{1*(5x)^3+3(5x)^2(-4y)+3(5x)(-4y)^2+1(-4y)^3}}}
still requiring a bit more simplifying to finish.