Removed. I made a mistake haha and someone made the correct one :)
Answer:
10k.
Step-by-step explanation:
1) if for the 1st position can be used 0-9 digits (10 digits), for the 2d - 0-9 digits, for the 3d - 0-9 digits and for the 4th - 0-9 digits, then
2) the required number of pwd is: 10*10*10*10=10⁴=10000.
The correct answer is 600. For area do you Base times height which is 20×30 which equals 60.