If voiture is feminine then isn't the use of longeur for wide correct. I was marked wrong.
Could you add the link to the related lesson or exercise please? It would make it easier to see which question from the kwiz / exercise you are referring to.
If you mean as an adjective, with voiture, it is < longue > not < longueur > (and not < long > either). Agreement needed.
With specific dimensions of the vehicle, the expressions:
As < être - dimension >, it is < (être) longue de (dimension)> Agreement needed
As < faire - dimension >, it is < (faire dimension) de long > or < de longueur > No agreement, just 2 different ways of expressing.
( There is a spelling error in your question, and that could also be marked incorrect if you were using < faire > )
Adding to Maarten's answer, notice that long/longue is an adjective whereas la longueur is a noun.
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