As at 2016, Parliament has a fixed term of 5 years. Originally there was no fixed limit on the length of a Parliament, but the Triennial Act 1694 set the maximum duration at three years. As the frequent elections were deemed inconvenient, the Septennial Act 1715 extended the maximum to seven years, but the Parliament Act 1911 reduced it to five. During the Second World War, the term was temporarily extended to ten years by Acts of Parliament. Since the end of the war the maximum has remained five years. Modern Parliaments, however, rarely continued for the maximum duration; normally, they were dissolved earlier. For instance, the 52nd, which assembled in 1997, was dissolved after four years. The Septennial Act was repealed by the Fixed-term Parliaments Act 2011. Summary history of terms of the Parliament of the United Kingdom
Question: How many years after the Triennial Act set the duration of Parliament to three years did the Septennial Act extend it to seven years?
Answer: 21