From the information given, this scenario creates a 45-45-90 triangle, allowing us to use the Pythagorean Theorem. 30^2+30^2=x^2. 30^2 is 900, so now you have 900+900=x^2. Add to make 1800=x^2. Now take the square root of both sides. It should come out to be about 42.43 meters.
Well, he will obviously be using 12 cups of pretzels, so let's set that aside. For every cup of pretzels, there are 3 cups of chex. So, multiply 3x12. That will give you how much chex you will need.