9/15+3/15
= 9+3/15
= 12/15
= 4/5 or decimal = 0.8
2/8+6/8
1/4+3/4
= 1
5/10-3/10
= 1/2-3/10
=1/5
5/8+3/8
= 5+3/8
= 8/8
Simplify by 8
I hope that's help !