In problems $15-18,$ rules are given for encoding a $6$ letter alphabet. For each problem:

$($a$)$ Is the encoding rule a function?

$($b$)$ Is the encoding rule one$-$to$-$one?

$($c$)$ Encode the word "bad."

$($d$)$ Write a table for decoding the encoded letters and use it to decode your answer to part $($c$).$

$($e$)$ Graph the encoding rule and the decoding rule. $($Fig$.12$ shows the graphs for the code in problem How are the encoding and decoding graphs related?

Please answer question $15$