How do i write this expression: the quantity seven plus z, squared

  (7+Z)²

Step-by-step explanation:

A less ambiguous way to describe the quantity might be "the square of the quantity seven plus Z".

As it is, we rely on the presence of the comma to tell us that the quantity to be squared is (7+Z). If the comma were not present, we would assume you want to add 7 to the square of Z: 7+Z².

  the quantity 7 plus Z: (7+Z)

  that quantity squared: (7+Z)²