Answer
3.5
Work Step by Step
$y=f(x)=33x^{-0.63}\\\\$
...Constant Multiple Rule:$\ \ \ [cf]^{\prime}(x)=cf^{\prime}(x)$
...Power Rule$:\ \ \ [x^{n}]^{\prime}=nx^{n-1 }$
$f^{\prime}(x)=33(-0.63x^{-1.63})=\displaystyle \frac{-20.79}{x^{1.63}}$
$f^{\prime}(a)$ is the rate of change of f(x) when x=a.
For a=3,
$f^{\prime}($3$)=\displaystyle \frac{-20.79}{3^{1.63}}\approx-3.46854109329\approx-3.5$
So the decrease in y is 3.5 percentage points.
