open (FILE, "<" ,"datafile");
my $sent_date="";
while (<>){
       my $this_date_range="";
       ($sent_date)=/^Sent: (.*)$/; #Could be more precise, but you're only expecting one instance of Sent at the start of a line ?
       ($this_date_range)= /^\*{4}\s+Analysis Date Range\s+:\s(\d{2}\/\d{2}\/\d{4})/;
        add_to_spreadsheet($sent_date,$this_date_range);
}