X can do a piece of work in 40 days; Y can do the same in 30 days. X started alone but left the work after 10 days, then Y worked at it for 10 days. Z finished the remaining work in 10 days. Z alone can do the whole work in?	Choices:
A) days
B) days
C) days
D) 1/2 days
E) days
Explanation:   10/40 + 10/30 + 10/x = 1   x = 24 days   daysnswer: days
<result>A</result>
X can do a piece of work in 40 days; Y can do the same in 30 days. X started alone but left the work after 10 days, then Y worked at it for 10 days. Z finished the remaining work in 10 days. Z alone can do the whole work in?