Answer:
4.74 hours
Step-by-step explanation:
Given that both person have to place same number of rivets that is
11209
first person take 9 hours to complete the work
hence 1 hour work of 1st person is of total work
second person takes 10 hours to complete the same work
hence 1 hour work of 2nd person is
Now if both work together then
1 hour work of both person = =
thus working together they need hours = 4.74 hours to complete the whole work which is placing 11209 rivets