The half life of carbon is 5700 years. if you started with 100g of carbon 14 how much would remain after 4 half lives

When dealing with a half life question, you should use the half life formula which is: y = a(b)^t/h

That result from subduction of oceanic plates beneath lighter continental plates. most of the earth's volcanoes are located around the pacific ring of fire because that the location of most of the earth's subduction zones.