Question 950091
Carlos oils all lanes/5 hrs= 1/5 of the lanes/hr.
Jenny oils all lanes/9 hrs=1/9 lanes per hour.
Together they oil 1/5 per hr+1/9 per hr=9/45 per hr+ 5/45 per hr=14/45 lanes per hr=0.311=31.1% of all lanes per hour
To do all lanes  1/0.311=3.21 hrs ANSWER: Together it takes Carlos and Jenny 3.21 hours to oil all the lanes.