input: Write a function to calculate the area of a hexagon.
  assert calculateArea(2) == 10.392304845413264
  assert calculateArea(5) == 64.9519052838329
  assert calculateArea(10) == 259.8076211353316
output: def calculateArea(side_length):
      import math
      return (3 * math.sqrt(3) / 2) * (side_length ** 2)