input: def solve_linear_equation_system(a, b, c):
      x = (c - b) / a
      y = (c - a*x) / b
      return x, y
  
  x, y = solve_linear_equation_system(2, 1, 4)
  print("x = {}, y = {}".format(x, y)) # x = 2.0, y = 2.0
output:     if a == 0 and b == 0:
          raise ValueError("Both coefficients a and b cannot be zero.")
      if a == 0:
          y = c / b
          x = 0
      elif b == 0:
          x = c / a
          y = 0
      else:
          x = (c - b) / a
          y = (c - a * x) / b
      return x, y