Answer:
[tex]4 {x}^{2} - 81 = 0 \\ 4 {x}^{2} = 81 \\ {x}^{2} = \frac{81}{4} \\ x = \sqrt{ \frac{81}{4} } \\ x = \frac{9}{2} \\ {x = 4.5}[/tex]
