1. **State the problem:** We are given a circle with center G and diameter CD. We need to find the measure of angle $\angle CB$. 2. **Recall important properties:** - The diameter of a circle subtends a right angle to any point on the circle. This means any angle formed by the diameter and a point on the circle is $90^\circ$. - The measure of an inscribed angle is half the measure of its intercepted arc. 3. **Analyze the given information:** - $CD$ is a diameter. - $\angle CAB = 77^\circ$ (angle at A between points C and B). - $\angle DAE = 28^\circ$ (angle at D between points A and E). 4. **Find $m\angle CB$:** Since $CD$ is a diameter, $\angle C B D$ is a right angle, so $m\angle C B D = 90^\circ$. 5. **Conclusion:** Therefore, the measure of $\angle CB$ (which is $\angle C B D$) is $$m\angle CB = 90^\circ.$$