Something like:

## Note: INDEX STARTS AT 0, I show day number here for convenience:
##     Day:      1,  2,  3,  4,   5, ...
my @start    = ( 7,  6,  7,  0,   9, ... );
my @stop     = (15, 16, 18,  0,  12, ... );
my @personal = ( 1,  1,  0,  0, 1.5, ... );

my (@daily, @busi, $daily_total, $busi_total, $pers_total);

# array indices start at zero:
for my $i (0..30) {
    next unless $stop[$i] > 0;

    $daily[$i] = $stop[$i] - $start[$i];
    $busi[$i]  = $daily[$i] - $personal[$i];
    $daily_total += $daily[$i];
    $busi_total  += $busi[$i];
    $pers_total  += $personal[$i];
}
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Update: Ninja'd by kennethk - oh well. Note that my solution will save the daily totals while kennethk's solution uses temporary variables. Use whichever is appropriate for your situation. (and do read the references provided by kennethk).