$11 for 30 days then how much money for a day?

You will get " eleven thirtieths " of a dollar each day.

That is approximately $0.37 per day. (37 cents a day)

How you actually calculated that?

I just did 11 / 30 in the calculator.

Just like:

three fourths of a dollar = 3/4 of a dollar = 0.75 of a dollar

eleven thirtieths of a dollar = 11/30 of a dollar ≈ 0.37 of a dollar