Discrete Algebra and Geometry.
Quite possibly dekagram = 10 grams.
A math expression is a collection of math terms
Well, Algebra IS Math, it's just a different part of math. For example, addition and subtraction are math, but they're differents parts of math.
bar modeling is math
A letter in math can stand for any number
Math is an abbreviation of mathematics: it is not an acronym. So the h does not stand for anything!
the letter L can stand for a variable.
it stands for milligrams
it stands for miles.