$6.$ Construct npda's that accept the following languages on

$\backslash$Sigma $=\{$a$,$b$,$c$\}$

: $($a$)$

L$=\{$a

n

b

$3$n

:n$>=0\}$

$.($b$)$

L$=\{$wcw

R

:w in $\{$a$,$b$\}$

$$

$\}$

$.($c$)$

L$=$