Answer
HOI increase: 33% (82.5% increase)
Work Step by Step
From (b): the HOI in the third quarter of 2006 = 40% (the lowest)
From (c): the HOI in the first quarter of 2009 = 73% (the highest)
The increase in the HOI $=73$% $-40$% $=33$%
Or, as a percent increase: $\displaystyle \frac{73\%-40\%}{40\%}=82.5\%$
