Three solutions
CodeSolution 3

# Code
```pythondata []
import pandas as pd
import re

def find_valid_emails(users: pd.DataFrame) -> pd.DataFrame:
    # Solution 1
    def is_valid(email):
        if '@' not in email or not email.endswith('.com'):
            return False 
        else:
            begin, domain = email.split('@')
            if not begin.isalnum() or not domain.split('.')[0].isalpha():
                return False 
        return True


    # Solution 2: Using regex
    def is_valid(email):
        pattern = r'^[a-zA-Z0-9]+@[a-zA-Z]+.com
        result = re.match(pattern, email)
        return bool(result)
    
   
    return users[users['email'].apply(is_valid)].\
                sort_values(by='user_id')
    
    
```

# Solution 3
```pythondata []
import pandas as pd
import re

def find_valid_emails(users: pd.DataFrame) -> pd.DataFrame:
    
    pattern = r'^[a-zA-Z0-9]+@[a-zA-Z]+.com'

    return users[users['email'].str.contains(pattern)].\
            sort_values(by='user_id')
    
```
['Pandas']