please jawab no 31 Dan 32

31. f(9) = 2x - 7
            = 2(9) - 7
            = 18 - 7
            = 11

32. f(7) = ax + b      = 16
            = a(7) + b    = 16
            = 3(7) +(-5) = 16
            = 21 - 5       = 16
    a = 3, b = -5

     a - b = 3 - (-5)
             = 3 + 5
             = 8