The absorbance of a solution of tryptophan measured at $280$ nm in a cuvette of $2.0$ cm path length is $0.56$ at pH $7$. The molar extinction coefficient $(\varepsilon)$ for tryptophan at $280$ nm is $5600$ $M^{-1}$ $cm^{-1}$ at pH $7$. The concentration of tryptophan (in $\mu M$) in the solution is __________
