"I must work hard."

Translation: Rhaid i fi weithio'n galed.

[Arthfoel]

In this sentence I inputted Mae rhaid i fi and not Rhaid i fi. I am unsure of the distinction or difference and would appreciate advice here?

[mizinamo]

For those who also have the same question: This sentence seems to have become duplicated somehow. In the copy at https://www.duolingo.com/comment/13301986 , toffidil got an answer from EllisVaughan which is worth reading.