I'm doing my homework for digital logic in logisim. I need to make function solver for this function: f(x,y) = 6*y-8+x in 4bit arithmetic.
Here is my solution but it is not working for some inputs. I don't know where I failed. I will be thankful if you can help me somehow :)
Thanks

Solution: ![enter image description here][1]


  [1]: https://i.sstatic.net/Ujtj7.png

Edit: it is working, for example for 0000 for X, and 0101 for Y, but it is not working for 0000 and 1101. I need to get solution for function above