Scenario: A housing development is built in the middle of a large forested area that was previously a reserve. The surrounding area contains several lakes and rivers. Question: Many of the houses have fireplaces that are 15 percent efficient and use 15 kg of wood to heat a room to 20 degrees (C) which is 68 degrees (F). Wanting to reduce their ecological footprint, several of the homeowners are considering switching to wood stoves that are 75 percent efficient. If they do change to using a wood stove, how many kg of wood will they save per use?