Answer:
27 hours
Explanation:
We are given the information that it takes 6 hours for 20 workers to seed 40 acres. This means that with 20 workers the rate is 40 acres in 6 hours, or 40/6 = 6.67 acres per hour. When we only have 10 workers, we only have half as many people, therefore the rate will be twice as slow, so with 10 workers, the rate is 6.67/2 = 3.34 acres/hour.
To find how long it takes to seed 90 acres we just need to divide 90 by the rate. 90/3.34 = 27 hours.
Hope this helped!