1. The problem statement, all variables and given/known data For how long would a 68 kg person have to swim at a fast crawl to use all the energy available in a typical fast food meal of burger, fries, and a drink? Assume 25% efficiency. 2. Relevant equations Fast food meal provides 1350 Cal or 5670 kJ A 68 kg person swimming at a fast crawl uses 800 W of metabolic power. 3. The attempt at a solution I'm having trouble just setting up the equation. I know that Change in Thermal Energy + Change in Chemical Energy = 0 because it is an isolated system, but I don't know where to go from here, nor do I know what units I need each part to be in.