Breakdown of Сколько банок у вас было?
вас
you (acc, pl/formal) / you (genitive, plural/formal)
у
at, by
сколько
how much / how long / as much / as many as
быть
to be
Questions & Answers about Сколько банок у вас было?
Why does банка become банок here?
The word Сколько (how many) requires the noun to be in the genitive plural. For feminine nouns ending in -а like банка (jar), you drop the -а to make the genitive plural. That leaves the awkward consonant cluster банк. To make it easier to pronounce, Russian inserts an о (a "fill vowel"), giving us банок.
Why does the verb было end in -о (neuter singular) if we are asking about plural jars?
When the subject of the sentence is a quantity word like Сколько (how many) or много (a lot), the past tense verb defaults to the neuter singular form было. It does not agree with the plural noun банок.
Why is the word for "you" in the form вас?
In Russian, we don't usually say "you had." Instead, we use the structure "by you was." The preposition у (by/at) always requires the noun or pronoun to be in the genitive case. The genitive form of вы (formal or plural you) is вас.
Why isn't the word есть used in this sentence?