715.

1) 1/4+1/6 = 3/12+2/12 = 5/12

2) 1/6+7/8 = 4/24+21/24 = 25/24 = 1 1/24

3) 3/10 + 2/15 = 9/30 + 4/30 = 13/30

4) 5/12 + 1/18 = 15/36 + 2/36 = 17/36

5) 3/20 + 11/30 = 9/60 +22/60 = 31/60

6) 1/30 + 2/45 = 3/90 + 4/90 = 7/90

1) 1/4+1/6 = (3+2)/12= 5/12

2) 1/6+7/8 = (4+21)/24= 25/24

3) 3/10 + 2/15 = (9+4)/30= 13/30

4) 5/12 + 1/18 = (15+2)/36= 17/36

5) 3/20 + 11/30 = (9+22)/60= 31/60

6) 1/30 + 2/45 = (3+4)/90= 7/90