Answer
$t = 0$ or $t=3$ or $t=-3$
Work Step by Step
$5t^3-45t = 0$
$5t ( t^2 - 9 ) = 0$
$5t (t-3)(t+3) = 0$
Therefore
$5t = 0$ or $t- 3 =0$ or $t+3=0$
$t = 0$ or $t=3$ or $t=-3$
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