Answer
$9t^2+t+3$
Work Step by Step
By combining like terms, the given expression, $
(7t^2-3t-6)+(2t^2+4t+9)
$, simplifies to
\begin{array}{l}
(7t^2+2t^2)+(-3t+4t)+(-6+9)
\\\\=
9t^2+t+3
.\end{array}
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