Actually, 45 meters were repaired more than planned every day, and only 20-5 = 15 (days) was actually used.

In this 15 day, 45× 15=675 (meters) was actually built more than planned, which means that this 675 meters was originally planned to be completed in 5 days.

Therefore, the original planned daily maintenance meter is: 675÷5= 135 (meters).

The comprehensive formula of column is 45× (20-5) ÷ 5 = 135 (m).