Answer:
<h2>C . 7 units</h2>Step-by-step explanation:
The question is lacking appropriate diagram. Find the diagram to the question attached.
From the diagram, it can be seen that AD = AB+BC+CD
Given the following
AD = 23units
AB = 4units
CD = 12units
To get C=BC, we will substitute the given segments into the expression above as shown;
23 = 4+BC+12
23 = BC + 4 + 12
23 = BC+16
Subtract 16 from both sides
23-16 = BC+16-16
7 = BC
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<em>Hence the length of segment BC is 7units.</em>
