I used GeoGebra and got 18.

I don't know how but this is apparently wrong

When using the quadratic formula, you can look in the square root and that is 9801-2c. So you take the 8001 from the problem and subtract it from 9801 and you get 1800. Then you divide 1800 in half getting 900 which is your answer.

Actually, it's 5040 because the question says product not sum.