Bonjour
20)
A = 10 - (2x + 5) = 10 - 2x - 5 = - 2x + 5
B = 10 + (2x - 5) = 10 + 2x - 5 = 2x + 5
C = 10 - (2x - 5) = 10 - 2x + 5 = - 2x + 15.
21)
A = 7 * (3x * 2) = 21x * 2 = 42x
B = 7 * (3x + 2) + 4 = 21x + 14 + 4 = 21x + 18
C = 7 + 3 (2x - 5) = 7 + 6x - 15 = 6x - 8