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The original price was x. So after the 10% discount the price was
. That price was then discounted 15%, so the price is now
, but we know this expression is equal to $306, because that is what was paid. So:
If the original price was 400, the 10% discount price would have been 400 - 40 = 360, then the 15% discount would have been 360 * .15 = 54, so the final price would be 360 - 54 = 306. Checks.