Answer: Do mind that I don’t completely trust that I am right, but I ask that you have faith in me.
So if I’m thinking correctly we subtract 180 from 217 which gives us 37. We then add that to 104 and subtract the sum from 180 which gives us b. So,
180-104+37
180-141=39
So b should equal 39 degrees, to check we add all the respective angles up,
104+39+37=180