Answer:
I think the answer is 2 dollars
Step-by-step explanation:
The total number of keys equals:
12 + 5 + 11 + 2 = 30 keys
The probability to pick a sliver key is:
12/30 = 2/5
The probability to pick a copper key is:
11/30
Hope that helps
To solve this problem you must apply the proccedure shown below:
If
, you have that:

Because
and 
Therefore, as you can see, the answer is: 