Answer:
16
Step-by-step explanation:
The two angle created by the bisector have equal measures, so ...
m∠ABD = m∠DBC
2y = 5y -12
0 = 3y -12
0 = y -4
4 = y
2y = 2·4 = 8
m∠ABC = 2×m∠ABD = 2×8
m∠ABC = 16
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We presume the angle measures are in degrees, though that is not specified by the problem given here. These numbers could all be radians, but 16 radians is more than a couple of times around the circle.
