Answer :
After 3 hours, Emerson will have worked 3 hours and dug 2 holes. Johnna will have worked 2 hours and dug 3 holes. So they'll need 1 more hole. Since Johnna works faster, we just need to add how much time she needs to dig 1 hole. It takes Johnna 120/3 = 40 minutes to dig 1 hole.
So they will finish digging after 3 hours and 40 minutes.
So they will finish digging after 3 hours and 40 minutes.
After 3 hours, Emerson will have worked 3 hours and dug 2 holes. Johnna will have worked 2 hours and dug 3 holes. So they'll need 1 more hole. Since Johnna works faster, we just need to add how much time she needs to dig 1 hole. It takes Johnna 120/3 = 40 minutes to dig 1 hole.
So they will finish digging after 3 hours and 40 minutes. :)