If I had the old-fashion camera that had a focal length of 35mm(0.035m) and I take a picture of a person 6 m away, how far does the film need to be from the lens to record a clear image?

I know that the equation is 1/f = 1/d(object) + 1/d(image) so would I do the following:
1/0.035m = 1/6 +1/unknown
28.57 = .1666+ 1/unknown
28.57-.1666=28.40
di=1/28.40 = .035m
Is this even close or all wrong-it doesn't sound correct

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