I'm not sure what you mean by calculate, whether you want to average them all or something else. However, one way to gather them all up so you can do what you want with them is this.

# We already have a filehandle open for reading. Read
# file line by line, putting data into a hash table.
#
our %averages = ();
while(<IN>)
{
    # Pick out the "average" lines with a regular
    # expression using () round brackets to remember
    # the "average1 or 2" (in $1) and the value ($2).
    #
    next unless /^(average\d+):\s+(\d+\.\d+)$/;
    push @{$averages{$1}}, $2;
}
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you end up with a hash table with keys "average1" and "average2" and the values being a list of the relevant values so that doing

print $averages{average1}->[0], "\n";
print $averages{average2}->[1], "\n";
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Would produce

3.2
5.0
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I hope this helps.

Cheers,

JohnGG