Given a = (1,2), B = (- 3,2), if Ka + B is parallel to a-3b, then the value of real number k is

Given a = (1,2), B = (- 3,2), if Ka + B is parallel to a-3b, then the value of real number k is

ka+b=(k-3,2k+2)
a-3b=(10,-4)
Ka + B is parallel to a-3b
-4(k-3)=10(2k+2)
k=-1/3