"The thinking employee is working slowly."
Translation:생각하는 회사원은 천천히 일하고 있어요.
Duo doesnt always take the whole sentence in consideration when giving hints.
correct me if i'm wrong, but from what i've gathered: 일하기 is a Noun made up of the VS of 일하다(to work) and the ending -기(which makes it a Noun) so "the working"
In this sentence however 일하고 있어요 means "is working", which is made up again of the VS of 일하다 and -고 있다 which puts the Verb before it in the progressive tense
hope it helps