difficult / hard, probably impossible

blind spot (place where the optic nerve attaches to the retina) / something overlooked, a point not noticed

to discover, to find (e.g. an error in a book) / to find (e.g. something missing)

to discover, to find (e.g. an error in a book); to find (e.g. something missing)

Alternative form of 見付ける

question, problem on homework etc. / a question; a matter (of time etc.) / a problem (something that needs to be dealt with); a trouble / an issue; a matter

(informal) no problem

unthinkable, out of the question

practical question (problem)

matter of life or death / (idiomatic) an extremely urgent matter