At 3:00 P.M., a bank robber is spotted driving north on I-15 at milepost 109. His speed is 140.0 mi/h. At 3:37 P.M., he is spotted at milepost 185 doing 104.0 mi/h. (Assume a straight highway). Assume north to be positive. What is his average velocity during this time interval? Enter a positive value if the direction is toward north and enter a negative value if the direction is toward south. mi/h