Answer: -7 and 3; -(x+7)(x-3)
Explanation:
seperate -4x to 3x - 7x
= (-x^2 + 3x) + (-7x+21)
for (-x^2 + 3x) factor out -x
for (-7x+21) factor out -7
= -x(x-3) - 7(x-3) factor out (x-3)
= (x-3) (-x-7) factor out the negative from (-x-7)
= -(x-3)(x+7)
if x = 3 => (3-3) = 0
if x = -7 => (7-7) = 0