The correct answer for this question would be option B) 18.8 units or the second option.
X^2 - 7x + 12 = 0
x^2 - 4x - 3x + 12 = 0
x (x - 4) -3 ( x - 4) = 0
(x - 4) (x - 3) = 0
x = 3 , 4
Check the answer by plugging in 3 and 4 for x, if the equation equals zero then you have your answer.
The plane will descend 900 ft every minute
This is the case because we divide 4500 by 5
Hope this helps and have a great day!