18 * (1/3 - 1/9 ) = 18 * 1/3 - 18 * 1/9 = 18/3 - 18/9 = 6 - 2 = 4
(2 - 3/4 - 4/5 ) * 20 = 2*20 - 3/4 *20 - 4/5 *20 = 40 - 60/4 - 80/5=
=40 - 15 -16= 40 - 31 = 9
(1 - 1/3 - 1/6 - 1/9 ) * 18 = 1*18 - 1/3 *18 - 1/6 *18 - 1/9 *18 =
= 18 - 6 - 3 - 2 = 18 - 11 = 7
(5/6 + 5/9 ) * 18/25 = 5/6 * 18/25 + 5/9 * 18/25 =
= 3/5 + 2/5 = 5/5 =1