(a): For congruences 2x = 7 (mod 11), find the smallest natural number x which satisfies it. (b): Suppose that (a, b, c) is a triple of integers. We call (a, b, c) a pythagorean triple if a^2 + b^2=c^2. Show that for any pythagorean triple (a, b, c) we have abc = 0 (mod 3) and abc = 0 (mod 4).