Answer
$\color{blue}{(5-4a+b)(16a^2+b^2-8ab+20a-5b+25)}$
Work Step by Step
With $125=5^3$, the given polynomial is equivalent to:
$=5^3-(4a-b)^3$
Factor using the formula $a^3-b^3=(a-b)(a^2+ab+b^2)$ with $a=5$ and $b=4a-b$ to obtain:
$=[5-(4a-b)][5^2+5(4a-b) + (4a-b)^2]
\\=(5-4a+b)[25+20a-5b+(16a^2-8ab+b^2)]
\\=(5-4a+b)(25+20a-5b+16a^2-8ab+b^2)
\\=\color{blue}{(5-4a+b)(16a^2+b^2-8ab+20a-5b+25)}$
