A $12.$ An orifice whose diameter is $100mm$ and $C=0\mathrm{.}92$ connects two tanks whose cross sections are $2m^2$ and $2\mathrm{.}5m^2$ respectively. If the $2m^2$ tank contains water $2\mathrm{.}1m$ higher than the other, how long would it take for both tanks to be in the same level?

a$.100\mathrm{.}62s$

b$.112\mathrm{.}35s$

c$.139\mathrm{.}69s$

d$.125\mathrm{.}36s$