After the political changes, in 1991, Bulgaria had a US$11.25 billion state debt, which represented 180% of the GDP. The state debt peaked in 1994, when it reached US$14.4 billion. During 1998-2008 Bulgaria maintained policy of Government budget balance, which reduced the state debt to 5.07 billion euro. Combined with the economic growth in that period, the state debt dropped to a record low of 13.7% of GDP, one of the lowest in the European Union. In 2008 Bulgaria also maintained 4.286 billion euro fiscal reserve, meaning that net state debt at this moment was only 0.784 billion euro. After the Financial crisis of 2007–08 Bulgaria turned to policy of Deficit spending and at the end of 2013 the state debt rose up to 7.219 billion euro, representing 18.1% of the GDP. In 2015, the debt rate increased further to 26.7% of the GDP, still remaining the third lowest in EU after Estonia and Luxembourg. Part of the increase was driven by the collapse of Corporate Commercial Bank in 2014, the fourth largest bank in the country, and the subsequent paying out of Deposit insurance.
Question: How many billions of dollars did the state debt increase from 1991 to 1994?
Answer: 3.15