A rough concrete $(n=0\mathrm{.}018)$ rectangular channel that has a bottom width of $3\mathrm{.}0$ feet and bottom slope of $1\mathrm{.}25\%.$ Calculate the normal depth for a flow of $50$ cfs $.$

$1\mathrm{.}5$ ft$.$

$2\mathrm{.}0$ ft$.$

$2\mathrm{.}5$ ft $.$

$3\mathrm{.}0$ ft $.$

$3\mathrm{.}5$ ft $.$