draw line l .draw a perpendicular to l at any point on l. on this perpendicular choose a point x,4cm away from l.through x,draw a line m parallel to l.
We need to follow the following steps-
Step 1: Draw a line l using scale of arbitrary length.
Step 2: Select any point say M on line l and at this point using compass draw a right angle to the line l.
Step 3: Using scale mark the point which is at 4 cm from M on the arm of right angle constructed to obtain the point N.
Step 4: Again at N, using compass draw a right angle on line MN in order to get the required line m.
The the corresponding angles are equal hence l||m.