Find a unit vector that points in the same direction as

a$)$ vec$(a)=($:$3,-9,1$:$)$ and vec$(w)=-5$vec$()+8$vec$()-2$vec$(k)$ compute $4$vec$(a)-5$vec$(w)$

b$)$ vec$(a)=($:$-7,9,-2$:$)$ and vec$(w)=5$vec$()+3$vec$(k)$ compute $7$vec$(a)-3$vec$(w)$