99x5 + 99x6 = 99x(5+6)
(5+4)+3 = 5+(4+3)
5x(3+2) = 5x3 + 5x2
3+2 = 2+3
7x(5x4) = (7x5)x4
71 - 31 = 75 - 35
976 - 856 = 980 - 860
5x3 = 3x5
