Question 12564
To solve any equation, you can use PEMDAS (Order of Operations) backwards.  First get rid of any subtraction and addition.
Add 19 to both sides.  3z-19+19=173+19  -->  3z=192
Then get rid of any multiplication and division.  
Divide both sides by 3.  3z/3=192/3 -->  z=64
Finally, plug your answer back in to make sure you did it right.
3(64)-19=192-19=173 We have the right answer!  :-)