A phone costs $600. A store offers a 15% discount, and then charges 8% sales tax on the discounted price. What is the final cost?

Apply the discount, then the tax on the discounted price. After the $15\%$ discount: $600(0.85)=510$ dollars. The $8\%$ sales tax on that price gives $510(1.08)=550.80$ dollars, choice C. Choice A ($510) is the price before tax. Choice D ($561) adds $10\%$ rather than $8\%$ to the discounted price. Choice B ($531) does not match any correct order of operations. The tax is charged on the discounted price, so apply the discount first.