As far as BEDMAS goes, the relevant thing here is that multiplication is performed before addition/subtraction - i.e., if I we use brackets to make the necessary order of operations clearer, it looks like:

Priming Effect = 12.739 + (2.530 * EAT) + (7.048 * BIS) + (1.41 * EATXBIS")

Which is still exactly the same equation. So if EAT = 1, BIS = 2 and EATXBIS = 3, you'd have:

Priming effect = 12.739 + 2.53*1 + 7.048*2 + 1.41*3

= 12.739 + 2.53 + 14.096 + 4.23

But keep in mind, if you have a statistical, financial, graphical or scientific calculator (or are working the answer out in Excel), you can simply type the original equation in as is (substituting in the actual EAT, BIS and EATXBIS figures) and it will use the correct order of operations and give you the right answer. This isn't the case for simple everyday calculators (the ones without fancy buttons) that do operations one at a time, though.