I have followed the instructions to go to Setup > Account Settings > Allow users to relate a contact to multiple accounts. However the "Allow users to relate a contact to multiple accounts" field is not there for me. I cannot select that options which is preventing me from completing the challenge.

I'm trying to  complete the following in my Salesforce Developer Edition:
Set Up Contacts to Multiple Accounts
Setup is quick and easy. Just follow these steps.
From Setup, enter Account Settings in the Quick Find box, then select Account Settings.
Select Allow users to relate a contact to multiple accounts.
Add the Related Contacts related list to the account page layouts your reps use.
From Setup, enter Accounts in the Quick Find box, then select Page Layouts.
Next to the appropriate page layout, click Edit.
Select Related Lists.
Drag Related Contacts onto the page layout. Because the Related Contacts related list automatically includes all direct contacts, you can remove the Contacts related list on your account page layouts.

There is no option under Account Settings to "relate a contact to multiple accounts".  Also Related Contacts is not an option for me under page layout.  Only "Related Content".  Am I just not able to complete these functions with my edition?  Please help so I can complete this module and figure this out!  Thanks!

 

Sharing this in case anyone else needs it.  Here is a formula field for clean company name. 

TRIM(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(Company, 
",", " ") /*remove commas*/,
".", " ") /*remove periods*/,
" inc", "") /*remove inc*/,
" Inc", "") /*remove Inc*/,
" INC", "") /*remove INC*/,
" llc", "") /*remove llc*/,
" Llc", "") /*remove Llc*/,
" LLC", "") /*remove LLC*/,
" Ltd", "") /*remove Ltd*/,
" LTD", "") /*remove LTD*/,
"Corporation", "") /*remove Corporation*/
)

If you have an improved version please post :)