Help!

I've seen these questions before. If these are homework problems, this is not a homework site!

Hey Lightning, $a=4$

$4x^2+12x+9\\ =(2x+3)^2$

I used: $(x+y)^2=x^2+2xy+y^2$

I saw the nine, so I know $y=3$

$2xy=12$, and $y=3$, so $x=2$

$2^2=4, a=4$

I hope this helped,

Gavin