Couple of ways to solve this for 'x' COmplete the square or Quadratic Formula
Completing the square:
x^2 + 4x - 16 = 0 Add 16 to both sides of the equation, then take 1/2 of the midle term,(4) square it and add it to both sides
x^2 + 4x + 4 = 16 + 4
(x+2)^2 = 20 Now take the sq rt of both sides
x+2 = + - sqrt (20) Now subtract 2 from both sides
x = -2 +- sqrt(20)