An investor can create a complete portfolio comprised of an S&P $500$ ETF and T$-$bills. The ETF has an expected rate of return of $8\%$ and a variance of $2\mathrm{.}40\%,$ and the T$-$bills have an expected return of $5\%.$ If the investor wishes to create a compete portfolio with an expected standard deviation of $17\%,$ how much of the complete portfolio should be invested in the S&P $500$ ETF?

$25\%$ ETF weight $50\%$

$50\%$ ETF weight $75\%$

$75\%$ ETF weight $100\%$

$100\%$ ETF weight