5.60×3= 16.8 (yuan).

Answer: It takes 1 1.2 yuan to buy two cups of coffee and 16.8 yuan to buy three cups.

(2) How much is a glass of juice more expensive than a glass of milk?

3.80-2.90=0.90 (yuan).

A glass of juice is 0.90 yuan more expensive than a glass of milk.