Factorise:

We have:

$36 c^{2}-(5 a+b)^{2}=(6 c)^{2}-(5 a+b)^{2}$

$=\{(6 c)+(5 a+b)\}\{(6 c)-(5 a+b)\}$

$=(6 c+5 a+b)(6 c-5 a-b)$

$\therefore 36 c^{2}-(5 a+b)^{2}=(6 c+5 a+b)(6 c-5 a-b)$