Question

draw a line segment pq=8.4cm.divide it into four equal parts,using ruler and compass

Answer 1

draw the perpendicular bisector of PQ
also
draw the perpendicular bisectors of the two equals parts
hence the line is divided into four parts.

Answer 2

steps of construction. pl follow accordingly.

1. draw the line segment PQ 
2. draw it's perpendicular bisector AB intersecting PQ at  C 
3. draw perpendicular bisector of PC and then of QC respectively 
4. you will get four equal parts of segment PQ.

hope this helps u !!