with a certain medical insurance policy, the customer must first pay an annual $100 deductible, and then the policy covers 80% of the costs of x-rays. The first insurance claims for a specific year are for two x-rays. The first x-ray cost $640, and the second x-ray cost $920. How much in total will he need to pay for these x-rays?

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First you need the total cost, so add your two x-ray costs. The insurance will pay 80% of that. OF is always a good clue that you are going to multiply.

80% OF your total cost
.80 x your total cost

That answer is how much the insurance will pay.
To find how much your dude is paying, subtract the amount the insurance is paying from the total cost. Then add your $100 deductible.

Throw an answer on here and I'll let you know if it's right.