Hint for this Weeks Puzzler

This is not going to seem like much of a hint but here goes.
Remember that time is a factor in all averages involving distance and speed.  D=RT.  Therefore also remember that even though the distance is the same to the New Mexico border whether you're going or coming, the time spent going the slower speed will be a lot longer, in fact seven times as long. This fact will skew your average toward the smaller speed.