Question

what does how much longer mean addition or subtraction

Answer 1

That would mean subtraction, as (example) 
Somebody has twenty inch paper. Another person has a ten inch paper. How much longer does that somebody's paper compare to another person's?
This means 20-10 = 10, so the answer to this is 10.

Hope this helps!

Answer 2

How much longer means subtraction, because how much longer is asking the length that one item is longer than the other, like a yardstick compared to a ruler, how much longer is the yardstick, something like that.


Hope this helps, and have a nice day!