How to use a solver function to solve matrix?

So I have an equation that goes something like N.*P + S.*P + E.*P + W.*P = Q N S E and W are coefficients, P is pressure changing with time. In terms of [A]*[x]=[b] its supposedly [coefficients]*[Pressure]=[Q]. How would I use a solver to translate the equation into these matrix terms?

[zephyr21]

Another way to phrase my question, how would I populate the A,x, and b matrices?