Question 16629
First you need to inverse the square root, 
Square 3x+6 ^2=3x+6. Now you've "canceled" the square.
But you have to do the same to 4 
4^2= 16
Now. 3x+6 = 16
= 3x+6-6  = 16-6
   3x     = 10
   3x/3   = 10/3
    x     = 10/3