After a tree has been chopped down and burned to ash, the carbon isotopes in the ash are found to have a 146C to 126C ratio of 1.300∙10-12. Experimental tests on the 146C atoms reveal that 146C is a beta emitter with a half-life of 5730 yr. At an archeological excavation, a skeleton is found next to some wood ash from a campfire. If 50.0 g of carbon from the ash emits electrons at a rate of 20.0 per hour, how long ago did the campfire burn?