easy / plain, simple

extraordinary, unusual

emergency

very; extremely / exceedingly; tremendously

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

stairs used in emergencies

state of emergency (unusually difficult or dangerous situation)

(informal) no problem

unthinkable, out of the question

practical question (problem)