What if my low-pass filter circuit has different R (ohms) and C (capacitance) values, and I'm using a 3rd order low pass filter? Do I add every resistor (R) and capacitance value (C)? Then I'd apply the formula?

1/[2*pi*(R1+R2+R3) * (c1+c2+c3) ]

Would that be right? ...

If I had another scenario with same values for R and C, do I need to add them as well?

This is the schematic I'm using: http://img810.imageshack.us/img8...

What's the cutoff frequency?

Thanks in advance.