It is planned to maintain 26 meters every day, 12 days.

It is known that the length of this road is 26× 12=3 12 (m).

When the road is actually repaired, it will be repaired for 3 days as planned and then for 3 days: 3×26=78 (m).

Not repaired, remaining: 3 12-78=234 (m)

Later, more 13m was repaired every day than originally planned. Later, it was actually repaired every day: 26+ 13 = 39(m).

Actual road repair days: 234÷39=6 (days)

It took another six days to finish this task.