Answer
$t = - 3$ OR $ t = 5$
Work Step by Step
$t^2-2t - 15 = 0$
$t^2 - 5t + 3t - 15 = 0$
$t(t-5) + 3 (t - 5)=0$
$(t+3)(t-5) = 0$
Therefore
$t + 3 = 0$ OR $t - 5 = 0$
$t = - 3$ OR $ t = 5$
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