A cup of coffee contains approximately 100mg of caffeine. when you drink the coffee, the caffeine is absorbed into the bloodstream, and is eventually...

A cup of coffee contains approximately 100mg of caffeine. when you drink the coffee, the caffeine is absorbed into the bloodstream, and is eventually metabolized by the body. Every 5 hours the amount of caffeine in the bloodstream is reduced by 50%.

1) Write an equation which expresses the amount of caffeine c milligrams in the bloodstream as an exponential function or the elapsed time t hours since drinking on cup of coffee.

2) How many hours does it take for the amount of caffeine to be reduced to 1mg and 10mg?