input: Write a function to solve the given linear equation system of the form: ax + by = c. Compute and return the values of x and y. If the equation system cannot be solved, return None.
  assert solve_linear_equation_system(2, 1, 4)==(2.0, 2.0)
  assert solve_linear_equation_system(1, 0, 3)==(3.0, None)
  assert solve_linear_equation_system(0, 1, 5)==(None, 5.0)
  assert solve_linear_equation_system(0, 0, 7)==None
output: def solve_linear_equation_system(a, b, c):
      if a != 0 and b != 0:
          x = c / a
          y = c / b
          return (x, y)
      elif a == 0 and b != 0:
          y = c / b
          return (None, y)
      elif a != 0 and b == 0:
          x = c / a
          return (x, None)
      else:
          return None