Answer:
18 people
Explanation:
Method A:
3 man-hours to stack 1 ton
36 tons is 36 times 1 ton, so it takes 36 times as long to stack.
36 * 3 man-hours to stack 36 * 1 ton, or
108 man-hours to stack 36 tons
To do the job in 6 hours instead of 108, you need to do 108/6 = 18 times as much work per hour, so you need 18 times as many people.
18 * 1 person = 18 people
Answer: 18 people
Method B:
1 person works 3 hours and stacks 1 ton. That same person works another 3 hours and stacks another ton. In a total of 6 hours, 1 person stacked 2 tons. Since you need 36 tons stacked in the same 6 hours, and 36 = 18 * 2, you need 18 times the number of people, so you need 18 people.