\(n_{CO_2}=\dfrac{6,6}{44}=0,15\left(mol\right)\\ n_{N_2}=\dfrac{3,36}{22,4}=0,15\left(mol\right)\\ n_{NO_2}=\dfrac{8,96}{22,4}=0,4\left(mol\right)\\ \overline{M}_X=\dfrac{m_X}{n_X}=\dfrac{0,15.44+0,15.28+0,4.46}{0,15+0,15+0,4}=\dfrac{29,2}{0,7}=\dfrac{292}{7}\left(\dfrac{g}{mol}\right)\\ \Rightarrow d_{\dfrac{X}{kk}}=\dfrac{\dfrac{292}{7}}{29}\approx1,438\)