string whatever = "Rundll32 Printui.dll,PrintUIEntry /ia /K /q /m \"SHARP MX-5500N PS\" /h \"Windows NT x86\" /v 3 /f sn0hwenu.inf";
or
string whatever = @"Rundll32 Printui.dll,PrintUIEntry /ia /K /q /m ""SHARP MX-5500N PS"" /h ""Windows NT x86"" /v 3 /f sn0hwenu.inf";