30.3+ 100.5 = 590, uphill and downhill ***590 km.
It takes 500/40= 12.5 hours to come back uphill, and 90/ 100=0.9 hours to go back downhill (note that going back uphill means coming back uphill), so it takes 8 hours to go to * * and 13.4 hours to come back.
Suppose you read page A on the fifth day, then (a+74+7 1+83+64)/5 +3.2=a, and the solution is a=77.