Both Oscar and Kim are correct and do have enough money to purchase the book.
Using Oscars way:
Multiply the original price by the discount 28.50 x 0.30 = 8.55
Take that amount and subtract it from the price 28.50 - 8.55 = 19.95
Then multiply the discounted price by the sales tax rate 19.95 x 0.10 = 1.995 = 2.00
Add the sales tax amount to get the final cost 19.95 + 2.00 = 21.95 total cost
Kim's way:
Subtracting the discount percent from 100 percent ypu get 70 percent, so multiplying the price by 70 percent will get you the sale price 28.50 x 0.70 = 19.95
Multiplying the sale price by 110 percent calculates the tax amount plus the price together to get the final cost 19.95 x 1.10 = 21945 = 21.95 total cost
Both Oscar and Kim are correct and do have enough money to purchase the book.