How to find a decimal equivalent to 39/50

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.)

Write the fraction 9/50 as a decimal if needed round to the nearest hundredth

A. 127 cm^2 b. 144.5 cm^2 c. 172 cm^2 d. 50 cm^2