Factorize each of the following algebraic expression:

$36 a^{2}+36 a+9$

$=9\left(4 \mathrm{a}^{2}+4 \mathrm{a}+1\right)$

$=9\left\{(2 \mathrm{a})^{2}+2 \times 2 \mathrm{a} \times 1+1^{2}\right\}$

$=9(2 \mathrm{a}+1)^{2}$

$=9(2 \mathrm{a}+1)(2 \mathrm{a}+1)$