input: def linear_eq(a: float, b: float, c: float) -> float:
      """ Calculate the objective function of a linear equation in the form ax + by = c.
      >>> linear_eq(3, 5, 7)
      0.0
      """
      return
output:     
      if a == 0 and b == 0:
          return float('inf') if c == 0 else float('-inf')
      elif a == 0:
          return c / b
      else:
          return c / a
  