Let $t$ be TNYWR.

What is the area of a triangle with base $2 t$ and height $2 t-6$ ?

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The area of a triangle with base $2 t$ and height $2 t-6$ is $\frac{1}{2}(2 t)(2 t-6)$ or $t(2 t-6)$.

The answer to (a) is 9 , so $t=9$ which means $t(2 t-6)=9(12)=108$.