Question $1.$ Find context$--$free grammars for $L=\{\begin{array}{c}{a}_{nbm}\text{:}n2m\\ n\end{array},m0$

$($Hint: consider odd$-$number $a\text{'}$s and even$-$number $a\text{'}$s$)$

Question $2.$

Construct the derivation tree for $(((a+b)**c))+a+b,$ using the grammar listed below $,$