Answer
$1259712x^2y^3$
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 $n=9,r=7$ and $4x,3y$): $_{9}C_7(4x)^{9-7}(3y)^7=36\cdot16x^2\cdot2187y^3=1259712x^2y^3$
