Question 257790
Here is the original problem:
(i) {{{4a^2+12ab+9b^2-25c^2}}}
look carefully, we really have this
(ii) {{{4a^2+12ab+9b^2}}}-{{{25c^2}}}
which is the difference of two squares. 
Factoring (ii), we get
{{{(2a+3b)^2}}} - {{{(5c)^2}}}
factoring as a difference of two squares, we get
{{{(2a+3b-5c)(2a+3b+5c)}}}