How many is 'six score' or a 'long hundred'?
Before the 15th century, Germanic languages called the number 120 'hundred'. Gradually, the English 100 became known as 'hundred' and the qualifier 'long' was added to the old 'hundred' (120). In archaic English, the number 120 was also known as 'six score'. A 'score' referred to the number 20, therefore 'six score' meant 'six times twenty', which equals 120.
Today, most of the western world uses decimal numbers or 'base-10 Arabic numerals'. Before the 15th century, many Germanic speaking countries used duodecimal systems in which today's 'ten' meant the number 12.
To avoid confusion in England, instead of referring to large numbers such as 120 as 'one hundred and twenty' or 'hundred', they spoke of the number in multiples of 20. Using the word 'score' to represent the number 20, larger numbers could be expressed as 'six score' (120), 'four score' (80), 'four score and seven' (87) and so forth.