What do you mean you can't do it? It'll be like shooting fish in a barrel!

你说干不了是什么意思？这不是小事一桩嘛！

《牛津词典》

They're shooting fish in a barrel.

他们是在桶里钓鱼。

youdao

Another expression is "as easy as shooting fish in a barrel."

VOA: special.2009.06.07

For Mr Rove, beating Mr Dean would have been like shooting fish in a barrel.

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For the SEC, going after the penny stocks trading on the Over-The Counter market is like shooting fish in a barrel.

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The sprawling Hill Country compound boasts five dwellings including a 9, 950-square foot main house, multiple garages, a mega indoor sports complex, a plethora of outdoor sports courts, skeet shooting, an archery area, and a seven-acre pond stocked with fish.

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