From M+O=6 and N+K=8, we get M+O+N+K=14. Since M+N+O+P+K=12, substituting gives 14+P=12, so P=-2. This is a system of linear equations where we can eliminate variables by combining equations. Adding M+O=6 and N+K=8 gives M+O+N+K=14, then comparing with the full equation.