Because the first letter of word "old" is "o" and "o" is a vowel pronunciation letter and we use with any vowel pronunciation letter article "an". So,here an old city is right.

Beauty is evergreen.

Right

I cannot talk to right now, I am in the hotel, I am going to eat food.

Right

In

Aviation means the flying or operating of aircraft.

wah mera bhai h.

m class me jitti hu.

Because "how much" is used for uncountable nouns and "how many" is used for countable nouns and car is a countable noun.So, we'll use here "how many cars are there?".