A fan delivers $225m^{\frac{3}{\frac{?}{?}}\text{m}\text{i}\text{n}}$ of standard air against a back pressure of $10$ cm of water whilc it is operating at $500$ rpm $.$ The efficiency of the fan is $85\%,$

$12\mathrm{.}81$ The power, in kW $,$ required to operate the fan is most nearly

a$.3\mathrm{.}7$

b$.4\mathrm{.}3$

c$.5\mathrm{.}6$

d$.6\mathrm{.}8$

$12\mathrm{.}82$ If the speed is increased to $700$ rpm how much power is required, and what is the new flow rate?

a$.7\mathrm{.}6$

b$.8\mathrm{.}5$

c$.10\mathrm{.}1$

d$.11\mathrm{.}9$