We need to subtract the area of the semicircle that was cut out of the paperboard from its original area.
The original area of the paperboard was the area of a rectangle 32in long and 24 in wide:

And the area of the semicircle, noticing that its radius r is 24in/2, is given by:

Thus, the area of the paperboard that remains is:

Therefore, the answer is 541.92 in².