12P10 means:
12 times 11 times 10 times 9 times 8 times 7 times 6 times 5 times 4 times 3.
12×11×10×9×8×7×6×5×4×3
Count them. there are 10 numbers written down starting with 12, then
1 less than 12, then 1 less than that, etc., and ending up with 3.
Now multiply those 10 numbers together with a calculator.
You'll get 239500800
That's the answer.
Edwin