Solution by Ruben Westerberg

ch-1.pl and ch-1.p6
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Run program to process guest log and display the amount of time lights are on

ch-2.pl and ch-2.p6
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Run the program with a RPN formated expression ( + - * / supported) as an argument (don't forget to quote).
Output is the result of the RPN expression. A default expression is used if no arguments are present