Calculate output voltage using the CMRR
The path gain or loss for a differential input amplifier are designed to be matched over the spectrum so that common mode input noise does not get converted to an equivalent differential mode input and appear at the output. This imbalance is called Common Mode Rejection Ratio.
Although it is referred to as a positive attenuation ratio it is a negative gain referenced to the input ratio, such that differential gain amplifies this imbalance to a single-ended output.
It is important to understand, the same CMRR imbalance exists on parasitic LC coupling on cables and board layouts so balance is important.
Given; \$~~~A_{dm} = 20 ~dB, ~~~CMRR = 90 ~dB,~~~ V_{cm-in} = -60~dBV  ~~~~~~~_{(Ref: ~0~dBV~=~1~V)}    \$
\$~~~~~A_{cm} ~[dB] = A_{dm}~ [dB] - CMRR~ [dB]   \$
\$V_{cm-out}~[dB] = A_{cm}~ [dB]  + V_{cm-in} ~[dB]   \$
\$ ~~~\therefore V_{cm-out} =  -130~dBV   =( 20 - 90 ) + (-60) \$
\$_{~~~~~~~~~~~~(Ref:~~~1 \mu V~ = ~- 120 ~dBV  ~~( = 20 ~log ~( 1~\mu V/1~V ) )}\$

This only applies to the ideal layout.

take note in future to determine all the factors that affect differential input impedance and balance error, as this limits your CMRR from component tolerances, parasitic coupling and differences in individual wire impedance to ground.