Question 82162
To see if it's an expression, just see if it makes any sense when verbalizing what it says.

{{{p(z+4)}}} "p times z plus 4" this is valid
p+/z "p plus divided by z" this makes no sense and is not an expression.
{{{zxp-4}}} "z times x times p minus 4" this is valid
{{{z+p+4}}} "z plus p plus 4"