Answer:
x^3 +9x^2 +27x +27
Explanation:
The expansion of a power of a binomial looks like ...
(a +b)^n = nC0·a^n·b^0 + nC1·a^(n-1)·b^1 + nC2·a^(n-2)·b^2 + ... + nC(n-1)·a^1·b^(n-1) + nCn·a^0·b^n
Of course, nCk = n!/(k!·(n-k)!) and a^0 = b^0 = 1. The list of coefficients nCk corresponds to a row of Pascal's triangle (see attached).
For n=3, this is ...
(a +b)^3 = a^3 +3a^2b +3ab^2 +b^3
You have a=x and b=3, so the expansion is ...
(x +3)^3 = x^3 +3·x^2·3 +3·x·3^2 +3^3
= x^3 +9x^2 +27x +27