Answer
Mass percentage of sulfur in the sample of ethyl mercaptan is 46.6 %.
Work Step by Step
Mass percentage of sulfur in the sample of ethyl mercaptan= $\frac{m(sulfur )}{m(ethyl mercaptan)}$ $\times$ 100%
Mass percentage of sulfur in the sample of ethyl mercaptan = $\frac{1.64 mg (sulfur )}{3.52 mg(ethyl mercaptan)}$ $\times$ 100%
Mass percentage of sulfur in the sample of ethyl mercaptan = 0.4659 $\times$ 100%
Mass percentage of sulfur in the sample of ethyl mercaptan is 46.59 % or 46.6 % ( to three significant figures).