The MacBook Pro 13 2.8GHz dual-core Intel Core i7 requires the use of ddr3 1600Mhz so-dimms in either 8 or 16GB configurations. The Maximum ram you can buy for this specific MacBook pro is 16GB.
The possible memory upgrade configurations are:
The MacBook Pro 13” 2.8GHz dual-core Intel Core i7 has 2 memory upgrade slots available for use. You will need to replace the factory installed memory if you wish to upgrade the ram.
The pulled ram can then be sold or traded in to further offset the cost of your upgrade.