解决 + 难题
难题 (nántí) is a noun meaning "difficult problem," "tough question," or "challenge." It refers to a problem that is hard to solve, and is used in academic, technical, and everyday contexts to describe something requiring significant effort.
这道数学难题我想了一个小时才解出来。
Zhè dào shùxué nántí wǒ xiǎng le yī gè xiǎoshí cái jiě chūlái.
I thought about this difficult math problem for an hour before solving it.
环境污染是全世界面对的难题。
Huánjìng wūrǎn shì quán shìjiè miànduì de nántí.
Environmental pollution is a difficult problem the whole world faces.
别担心,再大的难题我们都能一起解决。
Bié dānxīn, zài dà de nántí wǒmen dōu néng yīqǐ jiějué.
Don't worry — no matter how big the problem, we can solve it together.