Points A, B and C are collinear, AB = 15 cm, segment AC is 4 times segment BC. Find segment AC.

1. Let us denote the length of the segment BC by x.

2. Determine the length of the segment AC:

4 * x = 4x cm.

3. Since the length of the segment AB is 15 cm, then we compose and solve the equation:

4x + x = 15;

5x = 15;

x = 15: 5;

x = 3.

4. The length of the BC segment is x = 3 cm.

5. What is the length of the speaker section?

15 – 3 = 12 cm.

Answer: the length of the AC segment is 12 cm.