let's see idiom (also let me see/think)
让我想想看，让我想一想
used when you want to think carefully about something or are trying to remember
Next Saturday, let's see, that's when we're going to the theatre. 下周六，让我想想，那天我们要去看戏。
The last time I spoke to her was, now let me think, three weeks ago. 我上一次和她说话是，让我想想，3个星期以前。