Answer
$-64,481,508a^3$
Work Step by Step
The $r+1$ th term in the binomial expansion of $(x+y)^n$ is:
$\binom{n}{r}x^{n-r}y^r$
Here $x=a$, $y=-3$, $n=14$:
$r+1=12$
$r=11$
The indicated term is:
$\binom{14}{11}a^{14-11}(-3)^11=364a^3\times-177147=-64,481,508a^3$