Answer: The total amount William will pay for his purchase including tax is $14.24375.
Step-by-step explanation: Two notes books at $3.5 each plus $2.5 for pencils and $3.75 for a binder is $13.25. The sales tax of 7.5% multiplied by the $13.25 is 0.99375, and those added together equal $14.24375, William's total purchase price.