Simplify 23 + 5x + 7y – x – y – 27. Justify your steps.

23 + 5x + 7y – x – y – 27 original (given) statement

23 – 27 + 5x – x + 7y – y Commutative Property

(23 – 27) + (5x – x) + (7y – y) Associative Property

(–4) + (5x – x) + (7y – y) simplification (23 – 27 = –4)

(–4) + x(5 – 1) + y(7 – 1) Distributive Property

–4 + x(4) + y(6) simplification

–4 + 4x + 6y Commutative Property

I am lost when I reach the line in red:

(–4) + x(5 – 1) + y(7 – 1) Distributive Property

Where did that (1) come from, please?

-4 + (5) = 1

That is where I can find a 1...not sure how it got put in there, is all.

(And any advice on where to practice this?)

(Edit - this is supposed to be in Arithmetic forum, please move for me)