The vector that must be added to the vectors i^-2j^+3k^ and 6i^+3j^-7k^ so that the resultant vector is a unit vector along the Y-axis is
4i^+2j^+5k^
-7i^+4k^
3i^+4j^+5k^
null vector
j^=(i^-2j^+3k^)+(6i^+3j^-7k^)+C
Hence, C=-7i^+4k^