What was the total percentage change in exercise price for options granted between 2013 and 2016?
{"2 Jul 2013": {"Vesting Date": 2, "Expiry Date": 30, "Exercise Price $": 0.92, "No. of Options at Beg. of Year": 75000, "Options Exercised or Lapsed": -75000, "No. of Options at End of Year": "-"}, "2 Jul 2014": {"Vesting Date": 2.0, "Expiry Date": 2.0, "Exercise Price $": 1.3, "No. of Options at Beg. of Year": 470000.0, "Options Exercised or Lapsed": -205000.0, "No. of Options at End of Year": 265000.0}, "2 Jul 2015": {"Vesting Date": 2.0, "Expiry Date": 2.0, "Exercise Price $": 2.67, "No. of Options at Beg. of Year": 1000000.0, "Options Exercised or Lapsed": -75000.0, "No. of Options at End of Year": 925000.0}, "22 Dec 2016": {"Vesting Date": 31, "Expiry Date": 22, "Exercise Price $": 3.59, "No. of Options at Beg. of Year": 1323730, "Options Exercised or Lapsed": "-", "No. of Options at End of Year": 1323730}, "Total": {"Vesting Date": "", "Expiry Date": "", "Exercise Price $": "", "No. of Options at Beg. of Year": 2868730, "Options Exercised or Lapsed": -355000, "No. of Options at End of Year": 2513730}, "Weighted average exercise price": {"Vesting Date": "", "Expiry Date": "", "Exercise Price $": "", "No. of Options at Beg. of Year": "", "Options Exercised or Lapsed": 1.51, "No. of Options at End of Year": 3.01}}
exercise_price_2016 = df["22 Dec 2016"]["Exercise Price $"]
exercise_price_2013 = df["2 Jul 2013"]["Exercise Price $"]
answer = (exercise_price_2016 - exercise_price_2013) / exercise_price_2013 * 100.0