enquiry vs problem solving

enquiry and problem solving both are nouns.

Word	Noun	Adjective	Verb	Adverb
enquiry	Yes	No	No	No
problem solving	Yes	No	No	No

As nouns, problem solving is a hypernym of enquiry; that is, problem solving is a word with a broader meaning than enquiry:

enquiry (noun)	problem solving (noun)
a systematic investigation of a matter of public interest	the thought processes involved in solving a problem
a search for knowledge	the area of cognitive psychology that studies the processes involved in solving problems
an instance of questioning