difficult / hard, probably impossible

correspond to / be proportional to / suit, be appropriate for

suitable / worth / corresponding to/equivalent / more than average

quite; rather; considerably

corresponding / proportional / suitable, appropriate / substantial, considerable

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

set of problems

problem; point at issue

text that makes up a question/problem

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