Steps of construction:
1. Draw a line segment AB = 6 cm.
2. Make any acute angle at A. i.e. ∠CAB.
3. Starting from A as centre and any convenient radius set off 6 equal distances.
4. Join 6th arc to B.
5. Then we will draw line segment PM and QN parallel to OB.
Hence AN : NM : MB =1:2:3.