—Can you get the hot water to work? 熱水怎么開，你可以幫我嗎？
—Oh, a piece of cake... turn it, like that. 可以，很簡單。這樣擰一下。
—Thanks, I was having a rough time. 謝謝你，我不知道怎么做。

1. piece of cake=it's easy
—Do you know how to get there? 你知道怎么走嗎？
—Yeah, it's a piece of cake. 知道，很簡單。
—Go straight for a block, then turn right. 一路直走，然后右轉。

easy as pie/it's a cinch.

—Do you know how to open this?
—Yeah, it's cinch. Let me see it.

—Did you find the place OK?
—Yeah, it was easy as pie.

2. to have a rough time 做某事很困難

I'm having a rough time with this math problem. =I can't understand it.
He's never played ping pong before... so he's having a rough time.