B4. 1) ∠KOS - 3∠ROS = 20°, ∠KOS, ∠ROS - ?

1. ∠KOS - 3∠ROS = 20°. Let ∠ROS = x, then ∠KOS = 3x + 20°.
2. ∠KOR = ∠KOS + ∠ROS = (3x + 20°) + x = 4x + 20°.
3. If ∠KOR = 150°, then 4x + 20° = 150°. 4x = 130°. x = 32.5°. ∠ROS = 32.5°, ∠KOS = 3 * 32.5° + 20° = 97.5° + 20° = 117.5°.