If you travel at a constant speed, you follow this formula:

where s is the space traveled, v is the speed and t is the time passed. Knowing the speed and the desired space, we can solve the equation for the time:

Plug your values:

And two-thirds of an hour are 40 minutes.
To convert his speed in miles per minutes, you only need to use that one hour is composed of 60 minutes:
miles per minute