Simplify the following: (r+s-t) - (r-s+t)

R+s-t - (r-s+t)

=2s-t is the answer

People think this answer would be just = 2s but I have verified with an online calculator and the answer that textbooks look for regarding this is 2s-t

You would assume you would go r-r and thats 0 so no r's

you would say s - (-s) makes it plus and theres 2s

and you would say - t - (+t) is - t

that's why the answer is 2s-t

At first I also did t - (+t) and thought it would be no t's but the answer is in fact 2s-t