Explanation:

- The tower and flagstaff form a single vertical structure on a horizontal plane.

- The angle of elevation of the bottom of the flagstaff is 0°, meaning the observer is directly in line horizontally with the bottom of the flagstaff.

- The angle of elevation of the top of the flagstaff is 20°.

- Given the scenario, trigonometric identities are used to determine the height of the tower.

- h cos(2?): This represents the height as the horizontal component relative to the angle achieved when the tower and flagstaff are considered from the point of observation.

- h sin(2?): This would represent height based on a hypothetical 2? angle, irrelevant in the context.

- h cos ? and h sin ? are not directly relevant to the given scenario based on angles provided.

The correct answer is option 3: h cos(2?)