Answer:
4 hours
Step-by-step explanation:
Let time taken by Jim to rake be x hours
Jim's rate will be 1/x
Let y be time taken by Shirley to rake alone
Shirley's rate is 1/y which is equivalent to 1/3x since Shirley takes three times as long as Jim to imply Shirley's rate is slow
Total rate=1/x+1/3x=4/3x
Combined rate=4/3x which it takes them 3 hours hence a rate of 1/3
Therefore
4/3x=1/3
x=4 hours
