How to find the amount of sales tax Practice Test

If there is a 10% sale on an item, and then 9% sales tax is applied to that after-sale price, then what is the total cost of the item including tax as a percentage of its pre-sale sticker price?

Mike spent $30 on food and $50 on non-food products in the supermarket. There's a sales tax of 10% on non-food products only. How much did Mike spend in total at the supermarket?