To answer this, convert "3 miles per hour" to yards per minute."
Since 1 hour = 60 minutes, and 3 feet = 1 yard, we get the following:
3 mi 1 hr 5280 ft 1 yd
-------- * ------------ * ------------ * ------------ = 88 yards / minute (answer)
1 hr 60 min 1 mi 3 ft
Heather walked 88 yards per minute.