A scientist is measuring the amount of radioactive material in an unknown substance. When he begins measuring, there are 12.8 grams of radioactive substance. Nine days later, there are 7.33 grams. After 14 days, there are 5.38 grams. After 30 days, there are 2.00 grams. Assuming that the decay is exponential, find the equation that determines the number of grams remaining after x days and use the equation to determine the amount of radioactive material remaining after 50 days.