#### Answer

6

#### Work Step by Step

We are given that $f(x)=x^{2}-9$, $g(x)=2x$, and $h(x)=x-3$.
We are asked to find the value of $(f-g)(-3)$. We know that $(f-g)(x)=f(x)-g(x)$.
Therefore, $(f-g)(-3)=((-3)^{2}-9)-(2(-3))=(9-9)-(2\times-3)=(0)-(-6)=0+6=6$.