input: Write a function to solve a linear equation system of the form: ax + by = c which calculates the values of x and y given the coefficients a, b, and c. If the system is unsolvable (meaning a or b is zero and the corresponding term on the right side of the equation doesn't make sense), return None. The function should return the values of x and y as a tuple.
  assert solve_linear_equation_system(2, 1, 4) == (2.0, 0.0)
  assert solve_linear_equation_system(1, -1, 0) == (0.0, 0.0)
  assert solve_linear_equation_system(0, 3, 6) == (None, 2.0)
  assert solve_linear_equation_system(4, 0, 8) == (2.0, None)
  assert solve_linear_equation_system(0, 0, 0) == (None, None)
output: def solve_linear_equation_system(a, b, c):
      if a == 0 and b == 0:
          return None, None
      if a == 0:
          if b == 0:
              return None, None
          return None, c / b
      if b == 0:
          return c / a, None
      return c / a, 0.0