An unknown number.
Small/lower case 'x' means nothing in Roman Numerals. Capital 'X' means ' 10'. NB All the letters used in Roman Numerals are ALWAYS CAPITAL letters. Lower case letters do not mean a thing.
The SI nano- prefix means x 10-9
It doesn't stand for bananas.
3000
elementary maths
metre
It doesn't "stand for" anything. And wrong category.
maths economics comers
Answer In 1637, a very important book was published in France by Rene Descartes. he used the letter 'x', 'y','z' to stand for the unknown amounts in his maths problems. his book became very popular. other mathematicians followed his practice & started using the letter 'x' to denote the unknown.
LCM stand for Least Common Multiple
Base times Height
I guess you are referring to converting Roman Numerals to "normal" numbers: LXXVIII = L + X + X + V + I + I + I = 50 + 10 +10 + 5 + 1 + 1 + 1 = 78