Answer
$9a^2+30a+25$
Work Step by Step
RECALL:
$(x+y) ^2=x^2 +2xy +y^2$
Use the formula above where $x=3a$ and $y=5$ to obtain:
$=(3a)^2+2(3a)(5) +5^2
\\=9a^2+30a+25$
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