Answer:
Draw the line segment AB = 7 cm.
Draw ray BX making an acute ∠ABX.
Along BX. mark off five points B1, B2, B3, B4 and B5. Join B2 to A.
Through B5 draw B5P || B2A, intersecting BA produced at P.
The point P so obtained is the required point which divides AB externally in the ratio 3:5.