the formula to calculate the height is:
[tex]\begin{gathered} A=b.h\text{ but }from\text{ this formula }we\text{ find the height} \\ h=\frac{A}{b} \\ h=\frac{12}{9} \\ the\text{ answer is }\frac{12}{9} \\ \text{but }if\text{ we get the }third\text{ we have } \\ \frac{12}{9}\text{ }=\frac{4}{3} \end{gathered}[/tex]From the formula of the area we had to find a height for this, the base that multiplied the height happened to divide the area as you can see in the solution of the exercise.
the answer is
[tex]\frac{12}{9}\text{ units or this equivalent }\frac{4}{3}[/tex]