The annual return on the S&P $500$ Index was $16\mathrm{.}8$ percent. The annual T$-$bill yield during the same period was $4\mathrm{.}2$ percent. What was the market risk premium during that year?

$4\mathrm{.}2$ percent

$12\mathrm{.}6$ percent

$18\mathrm{.}1$ percent

$21\mathrm{.}0$ percent