Question

the square of a sum of a number and 3 is 16. There are two solutions

Answer 1

(x+3)^2 = 16
(x+3)(x+3) = 16
x^2 + 6x + 9 = 16
after subtracting 16 from each side you get...
x^2 + 6x - 7 = 0
(x+7)(x-1) = 0
so either (x+7) = 0, or (x-1)=0
x+7 = 0
x+7-7 = 0-7
x = -7
or x-1 = 0
x-1+1 = 0+1
x = 1
so...
x = -7 or x = 1

Answer 2

(x+3)^2 = 16

x+3 = +-4

x = 1 or -7