Coefficient of $x^5$ in the expansion of $(x+3)^6$ is

Question

Professor PC Thomas Classes · Answer

$T_{r+1} = { }^6C_r x^{6-r} 3^r$. For $x^5$, $6-r=5 \implies r=1$. Coefficient = ${ }^6C_1 3^1 = 18$.