solve the brackets first :
6 - (15) (8-8x) = 15
6- (120 -120x) = 15
then solve remove the bracket and solve the number:
-114 +120x = 15
then move the number (-114) to the right side of the equation:
120x = 129
solve the equation by diving 129 with 120:
x = 1 3/40