Bonjour
A = (3x + 7) (2x - 9) - (3x + 7) (5x - 7)
A = (3x - 7) [(2x - 9) - (5x - 7)]
A = (3x - 7) (2x - 9 - 5x + 7)
A = (3x - 7) (- 3x - 2)
A = (3x + 7) (2x - 9) - (3x + 7) (5x - 7)
A = 6x² - 27x + 14x - 63 -(15x² - 21x + 35x - 49)
A = 6x² - 27x + 14x - 63 - 15x² + 21x - 35x + 49
A = 6x² - 15x² + 14x + 21x - 35x - 27x - 63 + 49
A = - 9x² - 27x - 14
B = 25x² - 36
B = (5x - 6) (5x + 6)