bonjour
B = (3x + 7*2x - 5) - (3x + 7*5x - 7)
= (3x + 14x - 5) - (3x + 35x - 7)
= (17x - 5) - (38x - 7)
= 17x - 5 - 38x + 7
= 17x - 38x - 5 + 7
= -21x + 2
