Question

You mustn't/don't have to put on your evening dress

Answer 1

You don't have to put on your dress in the evening

Answer 2

You don't have to put on your evening dress .Ты не обязана надевать свое вечернее платье.
Обьяснение:
must -обязан
have to -обязан
Нельзя сказать You mustn't have to put on your evening dress.Это получается Ты не обязана обязана надевать вечернее платье.
Надо:Ты не обязана надевать вечернее платье.