An author receives $0.60 for each hardcover book or paperback book that is sold. there were x hardcover books and 38,000 paperback books sold of her most recent book. the author received a total of $51,000 for the book sales. the equation below can be used to determine the number of hardcover books that were sold.

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.