-b=3,1

It seems you've provided an equation, but it's not entirely clear what you're looking for. The notation "-b = 3,1" could imply a couple of things:

1. If you meant "-b = 3.1" (using a decimal), then you can solve for \( b \) by multiplying both sides by -1: \[ b = -3.1 \]

2. If the comma (",") indicates two separate equations or coordinates (like a point), please clarify what you mean or provide more context.

Please let me know how you would like to proceed!