"pretty easily" is correct and usable in written English. You would typically use this phrase to indicate that something is able to be done or completed without too much difficulty or effort. For example, "I was able to solve the problem pretty easily.".
We won pretty easily".
You date yourself pretty easily".
Two diaries fit together pretty easily.
"I blend in pretty easily," he said.
"I moved up pretty easily," she said.
"I blend in pretty easily," McEwing said.
The Trump balloon pops pretty easily.
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.