10.2#9

I got the answer but I don't know how to format it. It says that "Operands for '+' must be of the same type"

******************
That's because -6i+3j is a vector and you're trying to add 6z to it which is a scalar variable.  I think you meant to have +6k. Also, you do have the right direction but that vector has length √((-6)^2 + 3^2+6^2)=√(36+9+36)=√81=9, which is three times long as you want.