Помогите решить ! 31 и 33 Безотлагательно! !!

31)

(3a - 7b) - (-7a + 3b) = 9a - 42ab + 49b - 49a + 42ab - 9b = -40a + 40b = -40(a - b) = -40(a - b)(a + b) = ( при a=2.8; b=2.2) = -40(2,8-2,2)(2,8+2,2) = -40*0,6*5 = 120

33)

9a - 15b = 3(3a - 5b)

3m + mn = m(3 + n)

5ab - 5ac = 5a(b - c)

6a - 24ab = 6a(a - 4b)

x + x = x(x + 1)

28ab - 7ab = 7ab(4a - 1)

3a - 12a + 9a = 3a( 1 - 4a + 3a)

10xy + 25xy - 5xy = 5xy(2xy + 5x - xy)