A line with d.c’s proportional to (2,1,2) meets each of the lines  x=y+a=z and x+a=2y=2z. Then the coordinates of each of the points of intersection are given by

(t,t−a,t) is a point on first line and s−a,s2,s2 is point on second line, d r of line(s-a-t,s/2-t+a,s/2-t)given d.r is2,1,2s-a-t/2=s/2-t+a/1=s/2-t/2to find s and t