The Interstate On-Ramp Is $1.5 \mathrm{~km}$ West of Your Home, and on Leaving for Grandmother's House

The interstate on-ramp is $1.5 \mathrm{~km}$ west of your home, and on leaving for grandmother's house you are only able to accomplish an average velocity of $12 \mathrm{~km} / \mathrm{hr}$ between your home and the on-ramp. At the on-ramp, you wait for traffic for $2.0 \mathrm{~min}$ before proceeding toward grandmother's house. If you wish to arrive there, which is $15 \mathrm{~km}$ south of the on-ramp, 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?

A) $58 \mathrm{~km} / \mathrm{hr}$
B) $51 \mathrm{~km} / \mathrm{hr}$
C) $67 \mathrm{~km} / \mathrm{hr}$
D) none of these