Answer
See below.
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 $n=9,r=2$ and $x,2$: $_9C_2(x)^{9-2}2^2=36\cdot x^7\cdot4=144x^7$. Thus the coefficient is $144$.
