Answer:
15 minutes
Step-by-step explanation:
Their rate together is 1/6 floor per minute.
Her rate alone is 1/10 floor per minute.
His rate is the difference of these:
1/6 - 1/10 = 5/30 -3/30 = 2/30 = 1/15 . . . . floor per minute
It would take Jacob 15 minutes to do it alone.
