Kevin is taking a 600-mile trip, traveling at a rate of 50 miles per hour. How much faster must he travel to decrease his travel time by 4 hours?
First find his current travel time 600 miles / 50 miles per hour = 
<gadget id="calculator">600/50</gadget>
<output>12</output>
12 hours.
12 hours - 4 hours = 
<gadget id="calculator">12-4</gadget>
<output>8</output>
8 hours desired travel time
600 miles / 8 hours = 
<gadget id="calculator">600/8</gadget>
<output>75</output>
75 miles per hour.
75 miles per hour - 50 miles per hour = 
<gadget id="calculator">75-50</gadget>
<output>25</output>
25 miles per hour faster.

<result>25</result>