input: Write a function to calculate the sum of two variables using a lambda expression. Return the result of the summation.
  assert calculate_sum(3, 4) == 7
  assert calculate_sum(10, 20) == 30
  assert calculate_sum(0, 0) == 0
  assert calculate_sum(-5, 5) == 0
  assert calculate_sum(-3, -7) == -10
output: calculate_sum = lambda x, y: x + y