due to the absolute value, you need two equations
3x - 3 < or equal to 18 and 3x - 3 > or equal to -18
solve each equation by adding 3 to both sides and then divide by 3
3x<21 and 3x >-15
becomes x<7 and x>-5
written as a compound inequality -5 < x < 7 (or equal to)