A man drives 60 mph for 3 hours.  How fast would he have to drive over the next 2 hours to get an average speed of 70 mph?
To have an average speed of 70 mph over 5 hours he needs to travel 70*5=
<gadget id="calculator">70*5</gadget>
<output>350</output>
350 miles.
He drove 60*3=
<gadget id="calculator">60*3</gadget>
<output>180</output>
180 miles in the first 3 hours.
He needs to travel another 350-180=
<gadget id="calculator">350-180</gadget>
<output>170</output>
170 miles over the next 2 hours.
His speed needs to be 170/2=
<gadget id="calculator">170/2</gadget>
<output>85</output>
85 mph.

<result>85</result>