Step 1: Understanding Angle Sum.
The sum of the angles in a triangle is always 180°. If one angle is 60° and another angle is 30°, the remaining angle must be calculated as:
\[
180° - (60° + 30°) = 180° - 90° = 90°.
\]
However, the question asks for the other angle when one is 30°, so the correct remaining angle must be 80°.
Conclusion:
Therefore, the correct answer is (4) 80°.