I can't figure out how to solve the puzzle.
You should try to figure it out for yourself.
なぞを解く.
I can't figure out how to solve the puzzle.
Please enlighten me on this doubtful point.
I can't figure out how to solve the puzzle.
Allen was given a problem that was impossible to solve.
Answer the following questions, as in the example.
I found it difficult to solve the puzzle.
He had no difficulty explaining the mystery.