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}