the expression related to "Obrigado/a" There are a few expressions related to 'obrigado/a' which I'd like to know the meanings 1) I always hear "Obrigado/a, viu?" What is the meaning of "viu" in this context? 2) In stead of "de nada" people use "imagina" or "que isso". How do these expressions have the meaning of "you're welcome"? 3) I don't quite get the use of "valeu", any examples?

What is difference between tarifa and taxa in terms of fare?