Final answer:
The 'break' command is used to exit a loop and should be placed inside the loop where an 'if' statement can validate if the user input is '4'. When this condition is met, the loop will immediately terminate.
Step-by-step explanation:
The 'break' command should be placed inside the loop where it can check the condition if the user has entered '4'. Once the condition is met, the break command will terminate the loop and exit. For example, in a typical while or for loop, you would insert an if statement that checks if the user's input is '4', and if so, the break statement is executed:
while True:
user_input = input('Enter a number: ')
if user_input == '4':
break
# Other loop code
This will exit the loop immediately after '4' is entered.