Answer
$-t^4+2.5t^3-0.6t^2-9$
Work Step by Step
Removing the grouping symbols and then combining like terms, the given expression, $
(t^3-0.3t^2-20)-(t^4-1.5t^3+0.3t^2-11)
,$ simplifies to
\begin{array}{l}
t^3-0.3t^2-20-t^4+1.5t^3-0.3t^2+11
\\\\=
-t^4+(t^3+1.5t^3)+(-0.3t^2-0.3t^2)+(-20+11)
\\\\=
-t^4+2.5t^3-0.6t^2-9
.\end{array}
