a
\(\Delta {T_b}\, = \,\,\frac{{1000\,\, \times \,\,w\,\, \times \,\,{K_b}\, \times \,\,i}}{{m\,\, \times \,\,w}}\)

\( \Rightarrow \,\,2\,\, = \,\,\frac{{1000\,\, \times \,\,2.5\,\, \times \,\,0.76\,\, \times \,\,1}}{{m\,\, \times \,\,100}}\)

\(m\, = \,\,12.5\,\, \times \,\,0.76\)

\(\frac{{{P^0}\, - \,\,{P_s}}}{{{P^0}}}\,\, = \,\,\frac{n}{N}\)

\(\frac{{760\,\, - \,\,{P_s}}}{{760}}\,\, = \,\,\frac{{2.5}}{{12.5\,\,\, \times \,\,0.76}}\,\, \times \,\,\frac{{18}}{{100}}\,\,\,\)

\( \Rightarrow \,\,{P_s}\,\, = \,\,724\)