Salmon Noodle Casserole

2 T margarine or butter
2 T flour
1 tsp salt
1/2 tsp dry mustard
1 C milk
1 lb can red salmon, undrained
1-8 oz pkg Velveeta
2 C cooked noodles

Mix margarine, flour, salt, and mustard in a 3-quart saucepan over medium heat. Gradually stir in milk and cubed Velveeta, stirring constantly. When mixture is thickened, remove from heat and add undrained salmon and noodles. Place in 1-1/2 quart casserole dish and bake for 30 minutes at 350 degrees.