How many new bridges do we need to build in Königsberg to achive an Euler circuit? We know that an euler circuit in a graph is that the starting point and the ending point is the same and that we need to visit all bridge once how do i solve this problem? 

*Note that I am talking about the Königsberg of Eulers time and not the modern Kaliningrad.
Here's a solution from wikipedia:
https://en.wikipedia.org/wiki/Seven_Bridges_of_K%C3%B6nigsberg#Solutions
I guess this should be the answer to the problem.

Notice all the degrees are even.

So This is an Eulerian path.