Answer: the total length of road they built is 9 1/5 kilometers.
Explanation:
The total number of days that it took the construction crew to finish the road 2 4/5. Converting 2 4/5 days to improper fraction, it becomes 14/5 days.
If they built 3 2/7 kilometers of road each day, converting 3 2/7 kilometers to improper fraction, it becomes 23/7 kilometers.
Therefore, the total length of road that they built is
23/7 × 14/5 = 322/35 kilometers
Converting to mixed fraction, it becomes
9 1/5 kilometers