Answer:
81.9 hours.
Explanation:
5 work sites take 31.5 hours to prepare, so
1 work sites take 31.5 / 5 hours to prepare, and
13 work sites take . (31.5 * 13) / 5 hours to prepare
= 409.5 / 5
= 81.9 hours.
4.4m questions
5.6m answers