PSAT question - National Merit Scholarship qualification?

Well scores came in today for my school. I got a 64 in critical reading, 74 in math, and a 77 in writing for a total of 215. I'm pretty sure I have am a commended scholar, but how do I know if I am able to become a National Merit Scholarship Semifinalist? Also when will the decision/certificate or whatever the National Merit Corporation sends out be received by me?