If the total distance is 1, then1÷ (1/4+1/5) = 20/9 (hours).

2. Repair length on the second day =1/4 ÷ (1/4) =1km, and repair length on the first day = (1+1/4) *1= 5.

So the length of this section of highway is 1+5/4=9/4km.

3. According to the meaning of the question, in the second hour, the total length of 3/ 10 plus 5 kilometers was added, and 3/10+3//kloc-0 = 3/5 plus 5 kilometers was added.

Then 15+5=20(km) is the full length of 1-3/5=2/5.

So the distance between Party A and Party B = 20/(2/5) = 50km.