To find AC, we add lengths of AB and BC to get AC, which equals 7 units.
The student is solving a segment addition problem involving line segments.
We are given that B is between A and C, C is between B and D, BC equals 4 units, BD equals 12 units, and AD equals 15 units.
To find AC, we can use the fact that the lengths of the segments along a line add up to the total length of the line.
Since C is between B and D, adding BC and CD gives us BD:
BC + CD = BD
4 + CD = 12
CD = 12 - 4
CD = 8 units
Now we need to find AC. Knowing that A is between B and D, add AB and BD to get AD:
AB + BD = AD
AB + 12 = 15
AB = 15 - 12
AB = 3 units
Finally, add AB and BC to get AC:
AB + BC = AC
3 + 4 = 7 units