Nick starts with 20 milligrams of a radioactive substance. the amount of the substance decreases by 14 each week for a number of weeks, w. he writes the expression 20(14)w to find the amount of radioactive substance remaining after w weeks. autumn starts with 5 milligrams of a radioactive substance. the amount of the substance decreases by 50% each week for a number of weeks, w. she writes the expression (1? 0.5)w to find the amount of radioactive substance remaining after w weeks. use the drop-down menus to explain what each part of nick's and autumn's expressions mean.