Which equation shows how you can fing the number of minutes in one year

Initially 100 milligrams of a radioactive substance was present. after 6 hours the mass had decreased by 4%. if the rate of decay is proportional to the amount of the substance present at time t, find the amount remaining after 24 hours. (round your answer to one decimal place.)

If y varies directly as x2 and y=6 when x=6, find the constant of variation.

2.5 milligrams is equivalent to how many grams