A car is driving down a road at a normal speed of 50 miles per hour. It enters a hilly area of gradual incline and decline, wher
e it must drive 50 miles up hill and then 50 miles downhill. If this 100 mile section of road takes 2.6 hours to traverse instead of the expected 2 hours (the time it would take if the road was completely flat) determine the speed that the hills add or subtract when going over.
