Sorry, but this is a confusing and poorly-written question. You can get an answer that isn't even on the list if you interpret a certain way. The question doesn't specify whether this work schedule is cyclical or it just happened one time.
I interpreted it as if it happened one time:
Each worker completes 1/90 of a work per day individually.
Days 1-3: All three work together so they complete 3*(3/90) = 9/90
Day 4: A takes a break, B and C work together so they complete 1*(2/90) = 2/90
Day 5: All three work together again so they complete 1*(3/90) = 3/90
Day 6-7: Worker B takes a break so they complete 2*(2/90) = 4/90
Day 8-10: Worker C takes a break, A and B work together and complete 3*(2/90) = 6/90
So for the first 10 days they complete a total of 9 + 2 + 3 + 4 + 6 = 24/90 of the work, which means that they have an additional 66/90 to complete.
This is where the question breaks down. You can assume that they will go through the same cycle again OR you can assume that they will work together for the remainder of the time. If they work together they must complete (3/30)*x = 66/90 works. If you solve for x, you get x = 22. Add that to the first 10 days and the total is 32, which is not a choice.