The interstate on-ramp is 1.5 km West of your home, and on leaving for grandmother’s house you are only able to accomplish an average velocity of 12 km/hr between your home and the on-ramp. At the onramp, you wait for traffic, for 2.0 min – and then are able to proceed toward grandmother’s house. If you wish to arrive there, which is 15 km South of the onramp, over a river and through some woods, in a total elapsed time of 25.0 minutes, what average speed must you maintain on the interstate highway?