Simplify completely the quantity x squared plus x minus 12 over quantity x squared minus x minus 20 divided by the quantity 3 x squared minus 24 x plus 45 over quantity 12 x squared minus 48 x minus 60.

X² + x - 12 / x² - x - 20  ÷ 3x² - 24x + 45 / 12x² - 48x - 60

x² + x - 12 / x² - x - 20 * 12x² - 48x - 60 / 3x² - 24x + 45

(x² + x - 12)(12x² - 48x - 60)
(x² - x - 20)(3x² - 24x + 45)

12x^4 - 48x³ - 60x² + 12x³ - 48x² - 60x - 144x² + 576x + 720
3x^4 - 24x³ + 45x² - 3x³ + 24x² - 45x - 60x² + 480x - 900

12x^4 - 48x³ + 12x³ - 60x² - 48x² - 144x² - 60x + 576x + 720
3x^4 - 24x³ - 3x³ + 45x² + 24x² - 60x² - 45x + 480x - 900

12x^4 - 36x³ - 252x² + 516x + 720
3x^4 - 27x³ + 9x² + 435x - 900

12(x^4 - 3x³ - 21x² + 43x + 60)  
  3(x^4 - 9x³ + 3x² + 145x + 300)

4(x^4 - 3x³ - 21x² + 43x + 60)  
  (x^4 - 9x³ + 3x² + 145x + 300)

The correct answer is: b

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