Answer
$(4a+3)^2$
Work Step by Step
RECALL:
$A^2+2AB+B^2=(A+B)^2$
The given trinomial can be written as:
$=(4a)^2+2(4a)(3) + 3^2$
The expression above is a perfect square trinomial with $A=4a$ and $B=3$
Factor using the formula above to obtain:
$=(4a+3)^2$