Looks like it's a 45 degree tilt. You could also do a 30 degree tilt; both are on most 6" x 24" rulers and some 6" x 12" rulers.
When you have cut the borders, you will have bias edges on them.
Here's a little trick to help stabilize those biases. The graphic is not drawn exactly for your situation, but the idea still applies.
Jan in VA
Last edited by Jan in VA; 01-04-2015 at 02:56 PM.