1. Draw the line AC.

2. Construct the perpendicular bisector of AC using 2 circles with center at A and C, radius > half of AC

3. Draw a circle with r = 4.5 cm around the midpoint of AC.

4. Intersection points of this circle with the perpendicular bisector are B and D.

5. Complete the rhombus.

EDIT: I've attached the construction.