input: Write a function to solve a linear equation system of the form: ax + by = c. The function should take three arguments a, b, and c and return the values of x and y. If either a or b is zero, the function should return None.
  
  def solve_linear_equation_system(a, b, c):
      if a == 0 or b == 0:
          return None
      x = (c - b) / a
      y = (c - a * x) / b
      return x, y
  
  assert solve_linear_equation_system(2, 1, 4) == (2.0, 2.0)
  assert solve_linear_equation_system(1, 2, 5) == (3.0, 1.0)
  assert solve_linear_equation_system(0, 1, 2) == None
  assert solve_linear_equation_system(1, 0, 3) == None
  assert solve_linear_equation_system(3, 4, 10) == (2.0, 1.0)
output: def solve_linear_equation_system(a, b, c):
      if a == 0 or b == 0:
          return None
      x = (c - b) / a
      y = (c - a * x) / b
      return x, y