Answer
$=-2a^{4}+3a^{2}+9a$
Work Step by Step
$(a^{4}+5a)-(3a^{4}-3a^{2}-4a)$
$=a^{4}+5a-3a^{4}+3a^{2}+4a$
$=a^{4}-3a^{4}+3a^{2}+5a+4a$
$=-2a^{4}+3a^{2}+9a$
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