We can complete/finish this work in three hours.

They can complete/finish the same work in a day(or maybe 8 to 9 hours).

I joined the above two sentences like these:

We can complete the work in three hours that they do in one day.

Is this correct?
Could you tell me another way to say?

Close . . .

We can complete the same work in three hours that they can do in one day.

(it would be the same work, right?)
SusankayClose . . .
Thanks, Susankay.

Yes, I meant it's the same.
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My take:

They complete the work in a day which we can do in three hours
It takes them an entire day to do the work [that] we can complete in only three hours. (That is optional.)
Thanks, CG!
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Sounds native, GG.

I would've never come up with this if you hadn't told me.