What you'll see in the 3.0 Conversion Manual is that for total level, you should take class #1 and add one-third the level from any other classes. Thus, this PC should be converted to total level 13 + 4 = 17.
Therefore, some options are Clr9/Wiz8, or Clr13/Wiz4, or Clr4/Wiz13. If you use...