The sum of all the solutions of the equation $( 8 ) ^ { 2 x } - 16 \cdot ( 8 ) ^ { x } + 48 = 0$ is :\\ (1) $1 + \log _ { 8 } ( 6 )$\\ (2) $1 + \log _ { 6 } ( 8 )$\\ (3) $\log _ { 8 } ( 6 )$\\ (4) $\log _ { 8 } ( 4 )$