Can you answer this question?

This problem is very difficult.

The difficulty of this problem makes me scratch my head.

This problem is so difficult to solve, it gives me a headache.

Would you like to observe the stars at the observatory tonight?

Her dress was a vivid lemon color, and it stood out.

That proposal is completely unthinkable.

As a practical question, how are we going to fund this project?

He is observing stars at the observatory.

A new approach is needed to solve this set of problems.