Step 1: Understanding Rectangle Angles.
A rectangle has four right angles, each measuring 90°. This is because all the interior angles of a rectangle are right angles.
Step 2: Verifying the Options.
- Option (1): 60° is incorrect as a rectangle has right angles.
- Option (2): 70° is incorrect.
- Option (3): 90° is the correct angle between two adjacent sides of a rectangle.
- Option (4): 100° is incorrect.
Conclusion:
Therefore, the correct answer is (3) 90°.