Use a straightedge to draw line XY. Then construct line RS so that RS = 2XY

Answer 1

You do it. Can't do it here online. Sheesh. Now, if you want a description of the technique,

Pick a point P

with center at P, draw a circle with radius XY

Pick any point R on the circle

Draw the line PR, extended to intersect the circle at S.

Since PR + RS = XY + XY, RS = 2XY

Answer 2

Rats. Make that

Draw the line RP extended to S.

RP + PS = XY + XY