jmc

Expanding the desired expression, we get $(2a-3)(4b-6)=8ab-12a-12b+18=8ab-12(a+b)+18$. This implies that we need the sum and product of the roots of the given equation, which are $10/2=5$ and $5/2$, respectively. Thus, the desired expression equals $\left(8\cdot \frac{5}{2}\right)-(12\cdot 5)+18=\boxed{-22}$.