input: Write a function to calculate the objective function of a linear equation given by ax + by = c. Return the result of the objective function.
  def linear_eq(a, b, c, x, y):
      return a*x + b*y - c
  
  # Test cases:
  assert linear_eq(3, 5, 7, 2, 1) == 6
  assert linear_eq(1, 2, 3, 4, 5) == 19
  assert linear_eq(0, 0, 0, 0, 0) == 0
  assert linear_eq(-1, 1, 0, 3, -3) == 0
output: def linear_eq(a, b, c, x, y):
      return a*x + b*y - c