\(n_{C_2H_2Br_4}=\dfrac{17.3}{346}=0.05\left(mol\right)\)
\(C_2H_2+2Br_2\rightarrow C_2H_2Br_4\)
\(n_{C_2H_2}=0.05\left(mol\right)\)
\(m_{C_2H_2}=0.05\cdot26=1.3\left(g\right)\)
\(m_{CH_4}=4.33-1.3=3.03\left(g\right)\)
\(\%m_{C_2H_2}=\dfrac{1.3}{4.33}\cdot100\%=30.02\%\)
\(\%m_{CH_4}=69.98\%\)