What is the empirical formula of the polyethylene?
$1 \dfrac{\rm{mole(C)}}{\rm{mole(\ce{CO2})}}*\dfrac{7.217 ~\rm{g(CO2)}}{44.01 ~\rm g(\ce{CO2})/\rm{mole(\ce{CO2})}} = 0.1640 ~\rm{mole(C)}$

$2 \dfrac{\rm{mole(H)}}{\rm{mole(H2O)}}*\dfrac{2.955 ~\rm{g(H2O)}}{18.015 ~\rm g(\ce{H2O})/\rm{mole(\ce{H2O})}} = 0.3281~\rm{mole(H)}$

Since fewer moles of C, normalize on C

$\rm C = 1$

$\rm H = \dfrac{0.3281}{0.1640} = 2.000 $

So the empirical formula is $\ce{CH2}$