"How much food do you buy?"
Translation:Quot cibos emitis?
Quot is normally for something that can be counted, (quantus/quanti is for a an uncountable quantity), but in Latin "cibos" is not an uncountable, I think it's the explanation for "how much", and not "how many".
So, maybe a better translation, would be "How many meals do you buy?", as cibus" is also a meal, a dish, etc..., (but finally, it would be like asking how much food)
The English sentence as written talks about a singular mass of food. In Latin, this would require a partitive genitive ("genitive of the whole") construction.
I wrote Quantum cibi emis? which literally translates to "How much of (the) food do you buy?" This should be accepted, and it's a closer match to the English prompt than the plural solution that's currently offered.
Others are correct to note that Quot is only used for countable things, so Quot cibos emitis? would have to be translated "How many foods/meals do you buy?" or something like that.