input: Write a function to calculate the sum of two variables using lambda.
  assert sum_lambda(3, 4) == 7
  assert sum_lambda(0, 1) == 1
  assert sum_lambda(-5, 5) == 0
  assert sum_lambda(3.5, 4.5) == 8.0
  assert sum_lambda(-10, -5) == -15
output: sum_lambda = lambda x, y: x + y