Breakdown of Моя аудитория — номер пятнадцать, а его — шестнадцать.
он
he / it (for a masculine noun) / it (for a neuter noun)
а
and (contrastive)
мой
my (мой, моя, моё) / mine
номер
number (phone, room)
Questions & Answers about Моя аудитория — номер пятнадцать, а его — шестнадцать.
Why do we use dashes (—) twice in this sentence?
The first dash stands in for the verb 'is', since Russian doesn't use a present tense 'to be' verb. The second dash is used to avoid repeating words. It replaces the phrase аудитория номер (classroom number), so we don't have to say 'and his classroom is number sixteen'.
Is there a trick to pronouncing шестнадцать?
Yes, the т in the middle of шестнадцать is completely silent. You pronounce it like 'шес-НА-дцать'. Also notice that for numbers 15 to 19, the stress falls on the syllable just before the -дцать ending.
Why don't the numbers пятнадцать and шестнадцать change endings to match the feminine noun аудитория?
When you are just stating a number as a name or label (like room numbers, bus numbers, or page numbers), you use the basic dictionary form of the number. You don't need to make it agree with the gender of the noun.
Why does the sentence use а instead of и for the word 'and'?
The conjunction а is used to show contrast or comparison. Even though we translate it as 'and' in English here, it really means 'while' or 'whereas' (My classroom is fifteen, while his is sixteen). If you used и, it would sound like you are just adding items to a single list instead of contrasting two different rooms.