The phrase "relatively easily" is correct and usable in written English. This phrase is used to denote that something is not totally easy, but is still within the realm of possibility. For example: "I was able to complete the task relatively easily, despite the tight deadline.".
Relatively easily, say the scientists.
Companies can enter the market relatively easily.
That first smash came relatively easily.
Those ideas are relatively easily summarised.
Relatively easily as well, to 15.
But the logistical problems can be fixed relatively easily.
One part of "Spring Awakening" came relatively easily, however.
I love the desktop app, it’s always running on my Mac. Ludwig is the best English buddy, it answers my 100 queries per day and stays cool.
Cristina Valenza
Retail Lead Linguist @ Apple Inc.