$6\mathrm{.}99$ Compute the time required to reduce the depthi in the

tank shown in Fig. $6\mathrm{.}14$ by $1\mathrm{.}50$ m if the original depth is

$2\mathrm{.}68$ m $.$ The tank diameter is $2\mathrm{.}25$ m and the orifice diam$-$

eter is $50$ mm $.$