Answer:
[tex]60^\circ[/tex]
Step-by-step explanation:
Angle ABC is formed by two tangents drawn from point B outside the circle.
The measure of angle ABC is half the difference between the two intercepted arcs. One of those arcs is arc ADC, the big one with measure 240 degrees. The smaller arc, closer to point B, is arc AC with measure 120 degrees.
[tex]m\angle ABC=\frac{1}{2}(240^\circ - 120^\circ)=60^\circ[/tex]
To find out more, do an Internet search for "arcs and angles in circles".
