4. The equation of the line is written in the intercept form $\frac{x}{\frac{3}{a}}+\frac{y}{\frac{3}{2}}=1$. We read the intercepts on the coordinate axes as $m=\frac{3}{a}$ and $n=\frac{3}{2}$. The area of the right triangle is $\left|\frac{m \cdot n}{2}\right|=4.5$. Substituting the appropriate values, we get $\left|\frac{\frac{3}{a} \cdot \frac{3}{2}}{2}\right|=4.5$. From this, we calculate the parameter $a= \pm \frac{1}{2}$.

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4. The line given by the equation $2 a x+4 y-6=0$, together with the coordinate axes, forms a triangle with an area of 4.5. What can $a$ be?