Answer
$v(t)=-0.4t+1\quad $(percentage points per year)
Work Step by Step
We are given the 'acceleration' of percentage points ( which is $v'(t)$ )
$a(t)=-0.4$.
Then,
$v(t)=\displaystyle \int(-0.4)dt=-0.4t+C$
We are also given that at $t=0$ (the start of 2007)
$v(0)=1$
$1=-0+C$
$C=1$
so,
$v(t)=-0.4t+1\quad $( percentage points per year)
