First you want to get rid of the fraction number. Multiply each section of the compound inequality by 2:
2(-5)≤2(-3x+3/2)≤2(3)
-10≤-6x+3≤6
Now you want to isolate the x in the middle so subtract 3 from every part of the compound inequality:
-10-3≤-6x+3-3≤6-3
-13≤-6x≤3
Now divide every part by -6 - Remember that when you divide by a negative you have to switch the greater than or equal signs to less than or equal!
-13/-6≤-6x/-6≤3/-6
13/6≥x≥-1/2
Interval notation for this answer is [-1/2, 13/6]. If you need more help understanding interval notation, refer to this website: http://www.coolmath.com/algebra/07-solving-inequalities/03-interval-notation-01.htm