So 10% of $15.99 is 1.599 (You just move the decimal to the left once because of the one 0 in 10). So we know the discount is worth 1.599 cents.
$15.99
- 1.599
-------------
$ 14.391
Therefore, if the market price is $15.99, after the discount of 10%, the price will be approximately $14.39