This problem can be solved easily.
彼が成功したのは容易なことではない。
It was no easy thing for him to succeed.
That is not an easy task.
Achieving that goal is no easy matter.
This problem can be solved easily.
容易 is a formal, written-style word for 'easy', whereas 楽々 is a livelier, more colloquial adverb often paired with と.