Balance of trade is defined as imports subtracted from exports ( = exports - imports). Which of the following blocks of three years has witnessed the largest average negative balance of trade?

2007-2009
2007: 280 - 240 = 40
2008: 230 - 260 = -30
2009: 210 - 280 = -70
Average = (40 - 30 - 70)/3 = -20

2015 - 2017
2015: 200 - 310 = -110
2016: 220 - 250 = -30
2017: 200 - 240 = -40
Average = (-30 - 40 - 110)/2 = -60

2014 - 2016
2014: 200 - 320 = -120
2015: 200 - 310 = -110
2016: 220 - 250 = -30
Average = (-120 - 110 - 30)/3 = -86.67

2010 - 2012
2010: 200 - 310 = -110
2011: 220 - 290 = -70
2012: 210 - 320 = -110
Average = (-110 - 70 - 110)/3 = -96.67

Largest average negative balance of trade = -96.67, for the year 2010 - 2012.