[tex] {(3 - 2 \sqrt{3)} }^{3} + 3 {(2x + 5)}^{2} + 18x - 210 = {3}^{3} - 3 \times {3}^{2} \times 2 \sqrt{3} + 3 \times 3 \times {(2 \sqrt{3)} }^{2} - {(2 \sqrt{3)} }^{3} + 3(4 {x}^{2} + 20x + 25) + 18x - 210 = 27 - 54 \sqrt{3} + 108 - 24 \sqrt{3} + 12 {x}^{2} + 60x + 75 + 18x - 210 = 12 {x}^{2} + 78x - 78 \sqrt{ 3} [/tex]
[tex]x = \sqrt{3} [/tex]
[tex]12 {x}^{2} + 78x - 78 \sqrt{3} = 12 \times { \sqrt{3} }^{2} + 78 \sqrt{3} - 78 \sqrt{3} = 12 \times 3 = 36[/tex]
