Can someone explain how margin is suppose to fit into 400px ?

I know it equals 40px but I still don't understand

Please update the margin on this div, so that it will fit into 400px. +0 Please select the correct solution: Hint 1: Remember that this code: padding: 10px, puts 10 pixels of padding on all sides of the tag. Hint 2: ? Remember that this code: margin: 10px, puts 10 pixels of margin on all sides of the tag. Answer: ? 1

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