Right around 75 I would believe
12x^4+18x^2
= 3x^2 (4x^2+6)
Thus, the greatest common factor is 3x^2
3449995000 is what I got, I did 3.45x10^9 and then used that number and subtracted the answer from 0.5x10^4 to get the final answer, if that makes any sense.
The blank would be 50% because there are only 2 options it can land on and they are both even