Formula for the area of a parallelogram is
[tex]A=\text{height}\cdot \text{base}.[/tex]
If [tex]A=8\sqrt{90}\ un.^2[/tex] and [tex]\text{base}=2\sqrt{5}\ un.,[/tex] then
[tex]8\sqrt{90}=\text{height}\cdot 2\sqrt{5},\\ \\\text{height}=\dfrac{8\sqrt{90}}{2\sqrt{5}}=4\sqrt{\dfrac{90}{5}}=4\sqrt{18}=4\cdot 3\sqrt{2}=12\sqrt{2}\ un.[/tex]
Answer: the height has a length [tex]12\sqrt{2}\ un.[/tex]
