Learn Italian: Con la proroga, possiamo consegnare la ricevuta entro venerdì. - With the extension, we can deliver the receipt by Friday.

Entro is used specifically for deadlines, meaning "by" or "no later than". If you used fino a (until), it would imply a continuous action, meaning you would be in the process of delivering the receipt continuously until Friday, which doesn't make sense here!

What kind of extension is a proroga?

Proroga specifically refers to an extension of time or a postponement of a deadline. You will see this word a lot in Italian bureaucracy, such as when an office extends the deadline to pay a tax or submit a form.

Why is it just entro venerdì and not entro il venerdì?

In Italian, if you add the definite article il before a day of the week, it changes the meaning to a recurring event (like "on Fridays" or "every Friday"). Leaving the article out means you are talking about this specific upcoming Friday.

I sometimes mix up ricevuta and ricetta. How can I remember which is which?

Ricevuta is a "receipt" (proof of payment), which makes sense because it comes directly from the verb ricevere (to receive). Ricetta, on the other hand, means either a cooking "recipe" or a doctor's "prescription".