Marissa is hiking a 12-mile trail. She took 1 hour to walk the first 4 miles, then another hour to walk the next two miles. If she wants her average speed to be 4 miles per hour, what speed (in miles per hour) does she need to walk the remaining distance?
First figure out how many hours it takes to hike a 12-mile trail at 4 mph by dividing the distance by the speed: 12 miles / 4 mph = 
<gadget id="calculator">12/4</gadget>
<output>3</output>
3 hours.
Next subtract the time Marissa already spent walking to find out how much time she has left: 3 hours - 1 hour - 1 hour = 
<gadget id="calculator">3-1-1</gadget>
<output>1</output>
1 hour.
Now figure out how much distance she has left by subtracting the distance she already traveled from the total distance: 12 miles - 4 miles - 2 miles = 
<gadget id="calculator">12-4-2</gadget>
<output>6</output>
6 miles.
Now divide the remaining distance by the remaining time to find out how fast in miles per hour Marissa has to travel: 6 miles / 1 hour = 
<gadget id="calculator">6/1</gadget>
<output>6</output>
6 mph.

<result>6</result>