Given the following air sample data, calculate the gross activity airborne concentration in $C\frac{i}{c}{m}^3$ :

frisker $bkg=200cpm$

air sample volume $=60f{t}^3$

$1Ci=2\mathrm{.}22{10}^{6}dpm$

gross count rate on filter $=5,000cpm$

frisker efficiency $=12\mathrm{.}5\%$

filter efficiency $=90\%$

$1$ft$^3=2\mathrm{.}83$ x $10^4$ cm$^3$

a$.6\mathrm{.}7{10}^{-7}C\frac{i}{c}{m}^3$

b$.1\mathrm{.}1{10}^{-8}C\frac{i}{c}{m}^3$

c$.1\mathrm{.}4{10}^{-9}C\frac{i}{c}{m}^3$

d$.4\mathrm{.}4{10}^{-8}C\frac{i}{c}{m}^3$