You will get 345.4 g of HCl.
First of all, let's look at the equation
The coefficients in front of the formulas tell us the relative numbers of moles of each substance that are involved in the process. Specifically, because we see the same value (2) in front of the NaCl and the HCl, we know that each one mole of NaCl will theoretically produce one mole of HCl. (We'll deal with the 84.5% part later!)
Now, to find moles of NaCl, divide the given amount (655 g) by the molar mass of NaCl (found by adding the atomic molar masses of the two elements. You look this up on a periodic table, remember?).
This means we could get a theoretical limit of 11.20 mole of HCl. Since the actual yield in the reaction is 84.5%, we will in fact receive only
Finally, convert this to mass, by multiplying by the molar mass of HCl (36.5 g)