A single$-$effect evaporator is used to concentrate $9070k\frac{g}{h}$ of $10\%($wt$)$ NaOH solution entering at a temperature of $32\mathrm{.}2C$ to a final concentration of $40\%($wt$).$ Saturated steam used as the heating medium is at $1\mathrm{.}29$atm $($gauge$)$ pressure. The vapor space of the evaporator is at $118\mathrm{.}2mmHg$ absolute pressure and the overall heat transfer coefficient is $1400\frac{W}{m^{2\text{@}}}C.)=(1\mathrm{.}884\frac{kJ}{k}gC$

According to this, calculate

a$)$ The amount of steam used

b$)$ Heat transfer area

c$)$ The steam economy.