"What is the order of a group G generated by elements a and b subject only to the relations

[tex] a^7 = 1 [/tex] , [tex] b^3 = 1 [/tex] , [tex] ba = a^rb [/tex]"

I know that the order is the number of elements in the group.

I'm having a lot of trouble answering a lot of these questions.

Any help would be greatly appreciated.

Thanks in advance.