"rather easily" is correct and can be used in written English. It is used to describe something that can be done with little difficulty or effort. For example, "I was able to finish the project rather easily."
Game Djokovic, rather easily.
I have a rather easily identifiable name.
That's something I've adjusted to rather easily.
The subtext can be understood rather easily.
Johnson beat Wilson rather easily -- several times, in fact.
"The vast majority of cases settle and settle rather easily.
Before 2006, Iranian oil had been sold rather easily.
But analysts say Netflix will weather this storm rather easily.
As this roof has low stiffness and small mass, it vibrates and deforms rather easily.
We show here how exponential approximations can be rather easily designed.
In this paper, we show how exponential approximations can be rather easily designed.
Ludwig does not simply clarify my doubts with English writing, it enlightens my writing with new possibilities
Simone Ivan Conte
Software Engineer at Adobe, UK