For P(x1y1z1) and Q(x2y2z2)
Direction cosines are x2−x1PQ,y2−y1PQ,z2−z1PQ
Now for P(6,3,2),Q(5,1,4)
PQ=√(6−5)2+(3−1)2+(2−4)2=√1+4+4=3
And direction cosine 6−53,3−13,2−43=13,23,−23
And for A(3,−4,7),B(0,2,5)
AB=√(3−0)2+(−4−2)2+(7−2)2=√9+36+4=√49=7
Direction cosine is 3−07,−4−27,7−57=37,−67,27
∴k+m+n+l=1+2+3−6=0