Answer
$r \longrightarrow q$
Work Step by Step
Given:
$r$ = I'm registered
$q$ = I'm a citizen
$r$ = I vote
RECALL:
The English translation of $r \longrightarrow q$ is $q$ is necessary for $r$ (refer to age 125 of the textbook).
Thus, the symbolic form of the given statement is:
$r \longrightarrow q$