18_5/9 - 22_2/9 = 18_5/9 -21_11/9 = -3_6/9=-3_2/3
25_3/4 - 51_1/4 = 25_3/4 - 50_5/4 = - 25_2/4= -25_1/4
-6_2/9+1_2/3 = -6_2/9 + 1_6/9 = -5_11/9+1_6/9=-4_5/9
7_1/12 -8_3/4 = 7_1/12 - 8_9/12 = -1_8/12 = -1_2/3
18_5/6-7_1/2 = 18_5/6 - 7_3/6 = 11_2/6=11_1/3
2_1/5-4/15 = 2_3/15 - 4/15 = 1_18/15 - 4/15 = 1_14/15