1) 3/10 + 4/15 = 9/30 + 8/30 = 17/30
2) 11/21 - 7/14 = 22/42 - 21/42 = 1/42
3) 4 - 2*8/15 = 4/1 - 38/15 = 60/15 - 38/15 = 22/15 = 1*7/15
4) 3*5/9 + 4*11/18 = 7*21/18 = 8*3/18 = 8*1/6 или 3*5/9 + 4*11/18 = 32/9 + 83/18 = 64/18 + 83/18 = 147/18 = 8*3/18 = 8*1/6