use strict;
use warnings;

while (<DATA>) {
    chomp;
    s/^\s+//;
    s/\s+$//;
    my @tokens = split /\t/;
    if ((scalar @tokens) == 5) {
        print $_;
    }
    elsif ((scalar @tokens) == 3) {
        if (/number=(.*)/) { print "\t$1\n" }
    }
}

# not sure how many tabs you have in your 2nd line
__DATA__
Chr21    NT_113958    STS    76092    76265                
Chr21    NT_113958    number=1