According to the Inscribed Angle Theorem, the measure of an angle inscribed in a circle equals half the arc that it intercepts.
Then:
[tex]m\angle ABC=\frac{1}{2}m\overset{\frown}{AC}[/tex]
Since the measure of the arc AC is equal to 84º, then:
[tex]m\angle ABC=\frac{1}{2}(84º)=42º[/tex]
Therefore, the answer is:
The measure of ABC is 42º.
