I have two lines

r: [x,y]=[3,2]+t[4,-5]

q: [x,y]=[1,1]+s[7,k]

a) for what values of k are the lines perpendicular?

I got this by using the dot product of [4,-5].[7,k]=0 and then solving for k.

b) for what value of k are the lines paralell?

I'm not sure how to do this. I know the the normal vector is n=[A,B] and the direction vector is m=[B,-A].

so I took the dot product of [5,4].[7,k] =1

35+4k=1

k=-(34/4)

I made the dot product equal to 1 since cos 0 is 1.