a
\(\begin{array}{l}
Equation\,of\,trajectory\,is\,given\,as\\
\,\,\,\,\,\,\,\,\,\,y = 2x - 9{x^2}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,...\left( A \right)\\
\,\,\,Comparing\,with\,equation\,\,\,\,\,\,\,\,\,\,\,\,\\
\,\,\,\,\,\,\,\,\,y = \,X\,\tan \,\theta  - \frac{g}{{2{u^2}{{\cos }^2}\theta }} \cdot {x^2}\,\,\,\,...\left( B \right)\\
\,\,\,\,\,We\,get,\,\tan \,\theta  = 2\\
\,\,\,\,\,\,\therefore \,\cos \,\theta  = \frac{1}{{\sqrt 5 }}
\end{array}\)

\(\begin{array}{l}
Also,\,\frac{g}{{2{u^2}{{\cos }^2}\theta }} = 9\\
 \Rightarrow \,\,\frac{{10}}{{2 \times 9 \times {{\left( {\frac{1}{{\sqrt 5 }}} \right)}^2}}} = {u^2}\,;\,{u^2} = \frac{{25}}{g}\\
 \Rightarrow \,u = \frac{5}{3}\,m/s
\end{array}\)