Ben likes long bike rides. On one ride, he goes biking for six hours. For the rst hour, he bikes
at a speed of 15 miles per hour. For the next two hours, he bikes at a speed of 12 miles per
hour. He remembers biking 90 miles over the six hours. Compute the average speed, in miles
per hour, Ben biked during the last three hours of his trip.  Pick
A) 20
B) 35
C) 17
D) 51
E) 46
Ben biked 90-15- 2 * 12= 
<gadget id="calculator">90-15- 2 * 12</gadget>
<output>51</output>
51 miles over the last three hours, averaging a speed of   51/3= 
<gadget id="calculator">51/3</gadget>
<output>17</output>
17 miles per hour.   correct answer 17
<result>C</result>
Ben likes long bike rides. On one ride, he goes biking for six hours. For the rst hour, he bikes
at a speed of 15 miles per hour. For the next two hours, he bikes at a speed of 12 miles per
hour. He remembers biking 90 miles over the six hours. Compute the average speed, in miles
per hour, Ben biked during the last three hours of his trip.