Final answer:
To find the measure of AB, subtract the measure of BC from the measure of AC.
Step-by-step explanation:
To find the measure of AB, we can use the property of a straight line. The sum of the measures of the two smaller segments (AB and BC) is equal to the measure of the larger segment (AC).
So, the measure of AB can be found by subtracting the measure of BC from the measure of AC. In this case, AB = AC - BC, which is 32 - 20 = 12.