Answer
HOI decrease: 29% (42% decrease)
Work Step by Step
From (a): the HOI in the first quarter of 1999 = 69%
From (b): the HOI in the third quarter of 2006 = 40%
The decrease in the HOI $=69$% $-40$% $=29$%
Or, as a percent decrease: $\displaystyle \frac{69\%-40\%}{69\%}=42\%$
