Workload completed by Party B within 40 days: 40* 1/50=4/5.

The remaining workload is: 1-4/5= 1/5.

The time required to complete 1/5 workload a is:1/5/(1/75) =15 days.

So one left and one right: 40- 15=25 days.

2. X kilometers between the two places: x/25+x/ 15=4, and the result is 37.5 kilometers.