Assume that riding a bike burns 50 calories per mile. if you ride at a speed of 15 miles per hour, what is your average power output, in watts?

50 calories are consumed per milefor 15 miles per hour, calories consumed
= 50*15
=750 calories per hour, 
this is equal to 750/3600 
= 0.2083 calories/second, given that, 
1 calorie per sec 
= 4.19 watt, the average power output
= 0.2083*4.19
= 0.873 Watts