Answer
$12926067394240 x^9 y^6$
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 $n=15,r=6$ and $7x,2y$): $_{15}C_6(7x)^{15-6}(2y)^6=5005\cdot40353607x^9\cdot64y^6=12926067394240 x^9 y^6$
