math problem

x = 1/6 (6+sqrt(66))  AND  x = 1/6 (6-sqrt(66))

$3x(2x+1)-5=15x\\6x^2+3x-5=15x\\6x^2-12x-5=0\\a=6, b= -12, c=-5\\x=\frac{-(-12)\pm\sqrt{(-12)^2-4*(6)*(-5)}}{2*6}\\x=\frac{12\pm\sqrt{144+120}}{12}\\x=\frac{12\pm\sqrt4\sqrt66}{12}\\x=\frac{2(6\pm\sqrt66)}{12}\\x=\frac{6\pm\sqrt66}{6}$