How do you know when to use the subtraction property of equality as a reason as opposed to subtraction of real numbers?

You purchased 8 pounds 10 ounces of candy from a candy shop. you want to split it equally among 3 classrooms at a local school.

Avegetable garden and a surrounding path are shaped like a square that together are 11ft wide. the path is 2ft wide. find the total area of the vegetable garden and path

Lola says these two expressions have the same value. expression a expression b which explains whether lola is correct?