I dont think so. If ur citing from a book, newspaper.... everything should be written the same as what the book says. Hope it helps :)
Today is thursday and tomorrow is Friday
20% = 0.2
9 + 9 * 0.2 = 10.8 - Priya makes $ per hour.
100% - 15% = 85% = 0.85
10.8 * 0.85 = 9.18 - Siobhan makes $ per hour.
Answer: $9.18