I need help with this question pls

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.)

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15

The base of the rectangle pyramid is 13 inches long and 12 inches wide the height of the pyramid is 18 inches . what is the volume of the pyramid ?