Zhè hěn nán shuō.

这很难说。

It’s hard to say.

Note:

这(zhè): this

很(hěn): very

难(nán): difficult, hard

说(shuō): to say, to speak

Example:

A: 你觉得谁会赢？

    Nǐ juéde sheí huì yínɡ?

    Who do you think will win?

B: 这很难说。

    Zhè hěn nán shuō.

    It's hard to say.