How often does the man give his wife roses?

M: I’d dike some red roses.
W: Is it your wife’s birthday?
M: No, it’s our wedding anniversary. She really likes roses. So I give her some every week. I just wish they would stay fresh longer than they do.
W: If you put a little sugar in the water they will stay fresh for days.
M: Really? I want to try to use white vinegar in the water and it helped a little.
W: Sugar is even better.
M: It is worth trying, I will tell my wife. How much do I owe you?
W: Let’s see. They are $ 10 a dozen. So that will be $ 5.00.
M: OK. Here you are.
W: Thank you. Here are the flowers.