How to do this a=2i+3j-5k,b=mi+nj+12k and axb=0 then (m,n)?

Firstly find m,
Using the scalars of b to find (m,n). And axb=0
Now, b=m+n+12
Same as, 0=m+n+12 -------eq .1
Making m the subject,
m=-(n+12)= -n-12
Putting m into eq .1
-n-12+n+12=0
Therefore, m=0

Putting m into eq .1
0+n+12=0
n=-12