I want to say 5 but I'm not sure
Answer:
the same
Step-by-step explanation:
parralell lines are known for being straight forward and symetrical
I'm assuming you're trying to solve for r.
First divide a to both sides
Now you have

= a - r
Subtract a to both sides.
And then divide by -1 to both sides.
Now your equation is -

+ a = r