The amount of money saved in a bank account is often represented by the equation:

Where P is the initial amount of money deposited in the account and r is the rate in decimal form.
In this case, your equation looks like this:

Comparing the general equation with the one that you have, we can notice that the 650 is not raised to t like the P in the above equation, thus P equals $650.
Then, the value 650 represents that the initial amount in the account is $650.