Problem 9. (1 point) An unknown radioactive element decays into non-radioactive sub- stances according to the radioactive decay law dm = km where m is the mass of the radioactive material and k is a constant, called the decay constant. In 440 days the mass of radioactive ma- terial decreases by 70 percent. (a) What is the half-life of the element? (The half-life is the time required for 50 percent of the sample to decay) half-life: (days) (b) How long will it take for a sample of 100 mg to decay to 59 mg? time needed: (days) Answer(s) submitted: (incorrect)