If the discounted price is $499 and the discount is $13, the the original price (x) minus the discount ($13) equals the discounted price ($499).
Hence, x - $13 = $499.
PART B:
In order to find the original price (x) add the discount ($13) to the discounted price ($499). To do this, set the equation in Part A equal to x by add $13 to both sides.