headers already send means that there is out put to the page.
it is being reported at line 4:
output started at /homepages/20/d184490718/htdocs/YoungDesigns/quoteresponse.php:4
most likely, when you posted the code in you added a trialing space or a blank line after the closing php tag.
look for a blank like between the closing php tag and the next opening php tag:
or a blank space at the end of the closing php tag: