The top of the cardboard box measures 9 inches by 4 inches.
How much cardboard is needed
to make the top (only) of the box?
inches squared

The quantity of cardboard that is needed  to make the top of the box is:

Step-by-step explanation:

When the exercise asks you about the "inches squared," it's asking you about the area, the area of a rectangle (a rectangle because a cardboard box regularly is rectangular) is:

Now, you must replace the length and the width by the values in the exercise (doesn't matter what is width or length, remember the commutative property of the multiply):

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