The greatest number of friends who can receive a necklace is 6. The reason why is because 6 is the greatest common factor of 72 and 42.
Each friend will have 12 blue beads and 7 red beads. If you divide 6 (GCF) with both numbers you get 12 and 7.
Hope this helps :3
take your compass on a point on your line. then draw a circle. take the 2 points in which the circle hit the line and draw 2 circles larger than half the distance between he 2 points. take the point that they intersect and and connect it to the line and you point M and it is purpendicular. does that make sense?