X and Y together can complete a piece of work in 20 days, while Y and Z together can complete it in 24 days. After X worked on it for 10 days and Y for 18 days, Z alone completed the remaining work in another 13 days. X and Z together can complete 75% of the original in:
1
12 days
2
10 days
3
9 days
4
8 days