Answer
$(x+5)(x^{2}+3)$
Work Step by Step
Factor in pairs,
$x^{3}+5x^{2}+3x+15= (x^{3}+5x^{2})+(3x+15)=$
$=x^{2}(x+5)+3(x+5)$
$=x^{2}(x+5)+3(x+5)$
= $(x+5)(x^{2}+3)$
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