In the last 20 years geologists have begun measuring accumulation of helium (he) in some minerals because these minerals can retain he at temperatures up 100-200°c. the "date" gives a time when the material cooled below the temperature where the helium began to be retained, which is related to the depth of the material. where do you think the he comes from that allows this technique to work?

An electric power distributor charges residential customers $0.10 per kilowatt-hour (kwh). the company advertises that "green power" is available in 150 kwh blocks for an additional $4 per month. (green power is generated from solar, wind power, and methane sources.) if a certain customer uses an average of 391 kwh per month and commits to one monthly 150 kwh block of green power, what is her annual power bill