def serial_average(key = "001-12.43-56.78")
    serial = key[0,3]
    number1 = key[4, 5]
    number2 = key[10, 15]
    
    avg = (number1.to_f + number2.to_f) / 2
    avg = avg.round(2)
    key[4,11] = avg.to_s
    return key
end