kesulitan dalam menyelesaikan logaritma ini

6'log (x - 3) + 6'log (x + 7) - 6'log (3x - 1) = 1
6'log (x - 3)(x + 7)/(3x - 1) = 6'log 6
(x - 3)(x + 7)/(3x - 1) = 6
kalikan silang
(x - 3)(x + 7) = 6(3x - 1) 
x² + 4x - 21 = 18x - 6
x² + 4x - 18x - 21 + 6 = 0
x² - 14x - 15 = 0
(x - 15)(x + 1) = 0
x = 15 atau x = -1

HP = {15}