Answer
$9t^2-\dfrac{25}{16}$
Work Step by Step
Using $(a+b)(a-b)=a^2-b^2$ or the product of the sum and difference of like terms, the given expression, $
\left(3t-\dfrac{5}{4}\right)\left(3t+\dfrac{5}{4}\right)
,$ is equivalent to
\begin{array}{l}\require{cancel}
(3t)^2-\left(\dfrac{5}{4}\right)^2
\\\\=
9t^2-\dfrac{25}{16}
.\end{array}
