1) Here, [tex]b=12[/tex], so [tex](b/2)^{2}=(12/2)^{2}=\boxed{36}[/tex]
2) If we add 36 to both sides, we get [tex]x^{2}+12x+36=16 \longrightarrow \boxed{(x+6)}^{2}=16[/tex]
3) If we take the square root of both sides,
[tex]x+6=\pm 4\\x=-10, -2[/tex]