You'll likely be brought to a C, but it depends on the weight of the assignment on your grade. 50% weight? It'll bring you to a C or even D depending on how much you've done. 5%? Maybe you'll be knocked down to C but that's unlikely. 10% You'll probably be dropped down by a few percent.
Either way, I'd suggest you do your assignment, it's not worth the bad grade in the long run just because you don't want to do something. You can always reach out to me for help with it if you need.
