Answer:
AC = 7
Step-by-step explanation:
1. Draw out the line and label everything you know.
2. By observation, we know that AD is also equal to AC + CD.
3. To find CD, take the length of BD (12) and subtract it by the length of BC (4): 12 - 4 = 8. The length of CD is 8.
4. Finally, to find AC, subtract the length of CD (8) from AD (15): 15 - 8 = 7. The length of AC is 7.
