I need help with exercise 3 only. (a,b,c) please

The following are essay questions. Exercise 2. Consider the function h(x, y) - cos(7x + 13y). (A) Find k such that h(x, y) - k has no solutions. (B) Show that h(x, y) = 1 is a union of parallel lines. (C) Describe the level set h(z, y) = 1/3 Exercise 3. Put f(x, y) = x2 + y? - 10x - 20y. (A) Expand (x - 5)2 + (y - 10)2. (B) Show that for k > -125, the level set f(x, y) = k is a circle. (C) Describe the level set f (x, y) - -125