Answer:
Approximately 20 units (19.899)
Explanation:
Assuming that the length of line segment BO is equivalent to the length of line segment BA, both line segments together would be 36 units.
Then, it just becomes an instance of using Pythagorean Theorem (except we want to find a so we would do c^2 - b^2 = a^2).
36^2 = 1296 and 30^2 = 900.
1296 - 900 = 396.
The square root of 396 is 19.8997487... which can just be rounded as 20.
(sorry if this is wrong; I tried my best).