$2.$ Consider the following CFG

S $->$ Stmt

Stmt $->$ Var $=$ Expr

Expr $->$ Var $|$ Num $|$ Expr $+$ Expr $|$ Expr $$ Expr

Var $->$ a $|$ b $|$ c $||$ z

Num $->0|1|2||9$

Give the derivations fot the following strings:

$($a$)$ x $=5$

$($b$)$ y $=$ x $+3$

$($c$)$ z $=$ y $2$