Final answer:
The length of segment a is 19.5.
Step-by-step explanation:
To find the length of segment a, we can use the property that in a circle, two chords are equal if and only if they are equidistant from the center. Since segment b is given as 6.5 and segment c is given as 19.5, we can assume that they are equidistant from the center of the circle. This means that segment a is equal to segment c, so the length of segment a is also 19.5.