Need help on this thanks

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.)

Asphere has a diameter of 10 in. what is the volume of the sphere?

Find an equation of the line perpendicular to the graph of 28x-7y=9 that passes through the point at (4,1)