Certain building materials emit formaldehyde $($HCHO$),$ a toxic air pollutant. The following technique is proposed to determine the emissions rate.

$1.$ Place a sample of material that is to be tested in a CMFR$.$ Close the chamber. The chamber volume is V m$3.$

$2.$ Supply uncontaminated air into the chamber at a flow rate of Q m$3/$s$.$ Allow air to flow out of the chamber at the same rate.

$3.$ Monitor the HCHO concentration in the outlet air until a steady state concentration is reached Css $($g$/$ m$3)$

Given V$,$ Q$,$ and Css from such an experiment, what is the HCHO emission rate from the sample in $$g$/$s$?$ Assume HCHO is non$-$reactive $($i$.$e$.,$ does not undergo transformation within the CMFR$).$