Let $t$ be TNYWR.

What is the area of a triangle with base $2 t$ and height $3 t-1$ ?
The area of a triangle with base $2 t$ and height $3 t-1$ is $\frac{1}{2}(2 t)(3 t-1)$ or $t(3 t-1)$. Since the answer to (a) is 5 , then $t=5$, and so $t(3 t-1)=5(14)=70$.