1) 15/19 + 27/38 = (152) / (192) + 27/38
= 30/38 + 27/38
= (30 + 27) / 38
= 57/38

2) 9/16 + 19/24 = (93) / (163) + 19/24
= 27/48 + 19/24
= (27 + 38) / 48
= 46/48
= 23/24

3) 11/42 - 5/28 = (112) / (422) - 5/28
= 22/84 - 5/28
= (223) / (843) - 5/28
= 66/252 - 5/28
= (66 - 45) / 252
= 21/252
= 7/84

4) 13/60 - 7/40 = (132) / (602) - 7/40
= 26/120 - 7/40
= (263) / (1203) - 7/40
= 78/360 - 7/40
= (78 - 105) / 360
= -27/360
= -3/40