Thank you, Kyle! Your responses are always most helpful and provide for thought 😉
and this one prompted me to google "math expression," the definition of which has clarified everything for me ... it's the missing link!
I have been mistakenly interpreting a math expression as a number paired with its "unit" -- wrong, wrong, wrong! Without a sign of operation, it's just a number paired with its unit!
this from reference.com "An expression is a group of connected numbers, operations such as addition and multiplication, and unknown variables represented by letters of the alphabet."
Now I get it ... I feel a huge weight lifting!