input: Write a python function to compute the value of z given x and y where z = (x + y)**2 + (2 * x) - (3 * y).
  assert compute_z(2, 3) == 4
  assert compute_z(-1, 1) == -1
  assert compute_z(0, 0) == 0
output: def compute_z(x, y):
      return (x + y)**2 + (2 * x) - (3 * y)