Draw a line segment AB and by ruler and compasses obtain a line segment of length 3/4 AB.
Steps of construction:
Draw a line segment AB
With center A and radius more than 1/2 AB draw arcs one on each side of AB.
With center B and same radius draw arcs cutting previous arcs at P and Q respectively.
Join PQ and which intersect AB at C
With center C and radius more than 1/2 CB draw arcs, one on each side of CB.
With center B and same radius, draw arcs cutting previous arcs at R and * respectively.
Join RS and which intersect CB at D
AD = 3/4 AB.