He went to Glasgow and met with the Bishop of Glasgow, Robert Wishart. Rather than excommunicate Bruce, Wishart absolved him and urged people to rise in his support. They both then travelled to Scone, where they were met by Lamberton and other prominent churchmen and nobles. Less than seven weeks after the killing in Dumfries, at Scone Abbey on 25 March 1306, Robert Bruce was crowned as King Robert I of Scotland. He then began a new campaign to free his kingdom. After being defeated in battle, he was driven from the Scottish mainland as an outlaw. Bruce later came out of hiding in 1307. The Scots thronged to him, and he defeated the English in a number of battles. His forces continued to grow in strength, encouraged in part by the death of Edward I in July 1307. The Battle of Bannockburn in 1314 was an especially important Scottish victory. In 1320, the Declaration of Arbroath was sent by a group of Scottish nobles to the Pope affirming Scottish independence from England. Two similar declarations were also sent by the clergy and Robert I. In 1327, Edward II of England was deposed and killed. The invasion of the North of England by Robert the Bruce forced Edward III of England to sign the Treaty of Edinburgh-Northampton on 1 May 1328, which recognised the independence of Scotland with Bruce as King. To further seal the peace, Robert's son and heir David married the sister of Edward III.
Question: How many years was it between when the Treaty of Edinburgh-Northampton was signed and when Bruce came out of hiding?
Answer: 21