D - 4 miles per hour.
To get this, first, find how many feet she goes per hour. To get this, multiply 352 by 60 - or the number of feet per minute to how many minutes it takes to be an hour.
Once you get that, you now have how many feet you go per hour - 21,120. But, it's asking for miles per hour, so you need to convert it to miles. One mile compared to feet is 5,280 feet.
So in order to find how many miles that is, divide 21,120 by 5,280 which leaves you with 4.
Hope this helps!