Susan makes a purchase of $175 and is charged 7.75% for sales tax. What is the total cost of the purchase if Susan charges it on a credit card with a daily interest rate of 0.039% and pays the balance off at the end of 30 days?

First add sales tax: $175 × 1.0775 = $188.5625, or about $188.56. The 30-day interest rate is 0.039% × 30 = 1.17%, so the total is about $188.5625 × 1.0117 = $190.77. The best answer is $190.77.

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