3 leters
The phrase "one meter" contains eight letters. If you're asking about the number of letters in the word "meter," it has five letters. If you meant something else by "letters," please clarify!
1 barrel = 158.9 leters
Are you talking "liters" or "meters"? Are you talking about Kilo-meter? The prefix kilo means 1000. See if you can work that out, and while you're at it, try learning how to spell
500
7,600
35
11L
That is 0.341 litre
473.2 ml
800
1 litre (not leters!) = 1000 millilitres so 1.75 litres = 1750 millilitres. Simple!