For relations in your list of "Relations Needed", first put an identifying number (an Arabic numeral), then the equation, then the name or description of the relation (in parentheses), then (following and/or below the relation) definitions of any new symbols introduced in the relation. That is, use the general form:
(#) symbolic relation (name or description of relation)
or, when a new symbol is introduced:
(#) symbolic relation (name or description of relation), where symbol ≡ meaning or definition
For example:
(1) p = ρR_{d}T (the ideal gas law), where ρ ≡ density of the gas