1. Change all of the fractions to have the same denominator
3/10 = 18/60 (times by 6)
4/15 = 16/60 (times by 4)
7/20 = 21/60 (times by 3)
2. Add all the top numbers together
18+16+21 = 55
3. Answer is 55/60 as the denominator stays the same
4. If it needs simplifying then divide by 5 to get 11/12