input: Write a function to solve a linear equation system of the form: ax + by = c. The function should return the values of x and y as a tuple.
  def solve_linear_equation_system(a, b, c):
   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(3, -2, 7)==(3.0, -1.0)
  assert solve_linear_equation_system(1, 1, 5)==(5.0, 0.0)
  assert solve_linear_equation_system(0, 5, 10)==(2.0, float('nan'))
  assert solve_linear_equation_system(0, 0, 0)==(float('nan'), float('nan'))
output: def solve_linear_equation_system(a, b, c):
      if a == 0 and b == 0:
          return float('nan'), float('nan')
      if a == 0:
          return float('nan'), c / b
      x = (c - b) / a
      y = (c - a * x) / b
      return x, y