You meant 218, right?
No, I mean 228 - two hundred twenty-eight, not two hundred eighteen.
228 seats held by a Party - 10 margin of safety = 218 majority
Just because some Party has a slim majority of seats does not mean that they will be able to retain the Majority positions in the legislative house. History has shown that dirty tricks get played.
For example, don’t forget how the GOP “won” the California Assembly in the 1994 Election and “won” in the 2000 Election to retain control of the US Senate.