Rewrite the left hand side as the square binomial.

Question

X^2+4x+4=16
(X+ )^2=16

Answer 1

well (x+ a)^2 = x^2 + 2 a x + a^2 = x^2 + 4 x + 4
so
2 a = 4
AND
a^2 = 4
there is only one number like that, 2