Question

you mustn't smoke in the bus (begin you are not....)

Answer 1

$\bold{here \: is \: your \: answer.}$

You mustn't smoke in the bus...

To begin with " You are not"... Use words like
allowed , ordered etc. according to given sentence.

In the given sentence, we will write like this--

$You \: are \: not \: allowed \: to \: \\ smoke \: in \: the \: bus.$
_______________________________

$\bold{This \: is \: the \: answer}$
$\star{hope \: it \: helps \: you.} \star$

Answer 2

you are not allowed to smoke in the bus. ...