The adjective would be insoluble, unsolvable, or impossible.
"panacea"
Use the equation, speed = distance / time, substitute in the given information from the problem and solve it.
Sportsmanship is a word substitute for spirit of game
A verb meaning to make easier is facilitate.One meaning to make less complex is simplify.
There is no one-word substitute in English for "son-in-law."
A word substitute for the sentence "A fault that can be forgiven" is "venial".
what word can I substitute for constitutes
you can not substitute me. The director Substituted lead actor.
The word you want is florist.
The opposite of a problem (challenge, difficulty) could be a solution, answer, or fix.The opposite of the adjective problem could be easy, facile, or effortless.
By definition, an equation has a solution. The word comes from "equal". Some mathematical problems do not have solutions. For example, 1/0 = X is a problem with no solution. You know, in this example that there is no solution because of the "divide by zero" rule. Most insoluble problems are insoluble because of some rule that keeps you from moving ahead.
penniless