How to describe a level that is a bit harder than "a piece of cake"
An idiomatic expression which roughly means "it will take a little bit of effort to figure it out but not that hard" is "it's not rocket science".
TFD(idioms):
it's not rocket science
[be not rocket science]
To not be a pursuit, activity, or endeavor that requires extraordinary skill or intelligence.
Sure, it took a little bit of time to figure out, but reinstalling the modem wasn't rocket science or anything.Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.