20 7/18 - (15 5/6 - 9 25/27) = 20 7/18 - 15 5/6 + 9 25/27 =
= 367/18 - 95/6 + 268/27 =
=367*3/18*3 - 95*9/6*9 + 268*2/27*2 =
= 1101/54 - 855/54 + 536/54 = (1101-855+536)/54 =
= 782/54 = 14 26/54 = 14 13/27
