Question 313670
Do FOIL on the left side.


x^2 -5x + x -5 = 16
x^2 -4x - 21 = 0


Now ask yourself what two numbers multiply to -21 and have a difference of -4? -7 and 3.


x^2 -4x - 21 = 0
(x-7)(x+3)=0