Question

N order to write an expression like (5x + 4)3 in expanded form, it helps to look at (5x + 4) as just one number, n.

Answer 1

The expression (5x + 4)^3 in expanded form is 125 x3 + 300 x2 + 240 x + 64.  The expression will have also a root of x = -4/5. This is the form of trinomial expansion and can be  solve by multiplying the the term 3 times.