Assume that we have a straightedge with centimeter scale marked on it and a compass.
1. Mark a point A. From A, draw a ray approx. 10cm long rightwards, then also from A, draw an arc with the compass width of 7cm crossing the ray at B. So, line segment AB=7cm.
2. From A, draw a ray approx. 12cm long somewhat downwords, e.g. in the direction of 5 o'clock. Then also from A, draw 2 arcs** with radii 10cm and 6cm crossing the downward ray at C and D respectively. So that, AD:DC=6:4=3:2. Connect C to B.
3. From C, draw an arc with radius CD crossing BC at E. Keeping the compass width CD, draw an arc from D crossing AD at F.
4. From F, draw an arc rightwards with radius DE crossing the arc drawn from D at G. Then from D thru G, draw a ray crossing AB at H. Thus, we have: ∠ACB=∠ADH, so CB//DH. That is: AH:HB=AD:DC=3:2
Therefore, the point H devides segment AB in 3:2.
** If only the length of segment AB(=7cm) is available, try to divide the downward ray into 5 equal parts. From A, keeping the same compass width, e.g. approx. 2cm, step the compass downwards along the ray. Mark off 5 consecutive arcs. Label the 3rd crossing D, and the 5th C, so AD:DC=3:2 Connect C to B. Proceed to 3. above.