Answer
$16.07\%$
Work Step by Step
Number of moles of $NaOH$:
$0.550\ M\times 29.58\ mL=16.27\ mmol$
From stoichiometry:
$8.13\ mmol$ oxalic acid.
Mass of oxalic acid:
$8.13\ mmol\times 90.04\ mg/mmol=732\ mg$
Mass percentage:
$0.732/4.554\times 100\%=16.07\%$
