import pandas as pd
import numpy as np
df = pd.DataFrame({
    'EMPLID': [12, 13, 14, 15, 16, 17, 18],
    'V1': [2, 3, 4, 50, 6, 7, 8],
    'V2': [3, 3, 3, 3, 3, 3, 3],
    'V3': [7, 15, 8, 9, 10, 11, 12],
    'X': [2, 3, 1, 3, 3, 1, 2]
})
df['Y'] = np.where(df['X'] == 3, df['V3'], df['V1'])
print(df)