James takes up dancing for fitness.  He loses twice as many calories per hour as he did when he was walking.  He dances twice a day for .5 hours each time and he does this 4 times a week.  He burned 300 calories an hour walking.  How many calories does he lose a week from dancing?
He burns 2*300=
<gadget id="calculator">2*300</gadget>
<output>600</output>
600 calories an hour.
He dances for .5*2=
<gadget id="calculator">.5*2</gadget>
<output>1</output>
1 hour per day.
So he burns 600*1=
<gadget id="calculator">600</gadget>
<output>600</output>
600 calories per day.
So he burns 600*4=
<gadget id="calculator">600*4</gadget>
<output>2_400</output>
2400 calories per week.

<result>2_400</result>