The distance, say, a cart should be reversed (7)

I believe the answer is:

yardage

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'the distance' is the definition.
(yardage is a kind of distance)

I don't understand the remainder of the clue.

(Other definitions for yardage that I've seen before include "Length in units of three feet" , "measure" , "Distance in three-foot units" , "Quantity of fabric" , "Distance sometimes measured in paces" .)

I've seen this clue in The Daily Mail.

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