Is formal Letter important for class 6th. ?

Yes , ofcourse. Formal letter is very important for all the students irrespective of class as it is often used in our daily life. For example , it is mainly used in school for writing leave application,etc ; in offices formal letter are needed. So basically formal letters are important to learn.

Ayman Qadri is teaching following classes

Yes It is very important to learn the format to get good marks