the economic problems of the inner city.

内城的经济问题。

I do not have a simple solution to the drug problem.

我并没有解决毒品问题的简单方法。

The main problem is unemployment.

主要问题是失业。

He told Americans that solving the energy problem was very important.

他告诉美国人，解决能源问题十分重要。

With mathematical problems, you can save time by approximating.

对于数学题，你可以用近似值的方法节省时间。