if you look at the angle from the side you will understand that the length for angle section for both the beam and the column flange is the same that is 210 mm but as we are taking out the lateral dimension while the beam connection is being designed (150 mm)the same way the min lateral length for column connection is 2 times the edge distance (80mm) as there is one one bolt row on each angle . but there is nearest angle section is 150x75x10 mm but since it is not satisfactory we take 150x115x10mm of depth 210mm vertically downward. hope this helps.
210mm length aane par 150mm length wala angle section kese lga sakte h
if you look at the angle from the side you will understand that the length for angle section for both the beam and the column flange is the same that is 210 mm but as we are taking out the lateral dimension while the beam connection is being designed (150 mm)the same way the min lateral length for column connection is 2 times the edge distance (80mm) as there is one one bolt row on each angle . but there is nearest angle section is 150x75x10 mm but since it is not satisfactory we take 150x115x10mm of depth 210mm vertically downward. hope this helps.
How the gauge = 90 for both sections, how to calculate this gauge
From steel table