In the infrared spectra of styrene$/$acrylonitrile copolymers, the ratio of the absorbances of the $C-=N$ nitrile stretching vibration at $2250cm-1$ and the polystyrene aromatic ring$-$stretching vibration at $1600cm-1$ may be employed as a measure of the composition. Infrared analysis of a number of styrene$/$acrylonitrile copolymers of known compositions yielded the results listed in Table $1$ below. The infrared spectrum of a sample of poly$($styrene$-$co$-$acrylonitrile$)$ of unknown composition was recorded. The absorbance values at $2250$ and $1600cm-1$ in this spectrum were $0\mathrm{.}42$ and $0\mathrm{.}15,$ respectively. Estimate the composition of this sample

Table $1.$ Infrared analysis data obtained for a number of styrene$/$acrylonitrile copolymers

$\backslash$table$[[\backslash$table$[[$Acrylonitrile$],[$concentration$],[(\%)$