Answer:
Step-by-step explanation:
[tex](3x+15)\\\\3x+15\\\\\mathrm{Rewrite\:}15\mathrm{\:as\:}3\times\:5\\\\=3x+3\times\:5\\\\\mathrm{Factor\:out\:common\:term\:}3\\\\=3\left(x+5\right)[/tex]