Answer
$-4330260000x^3y^9$
Work Step by Step
According to the Binomial Theorem we can obtain the $r+1$th term of the expansion of the binomial $(x+y)^n$ by the formula $_nC_rx^{n-r}y^r$.
Hence here it is: (by plugging in $n=12,r=9$ and $10x,-3y$): $_{12}C_9(10x)^{12-9}(-3y)^9=220\cdot1000x^3\cdot-19683y^9=-4330260000x^3y^9$
