The correct answer is A. She incorrectly combined the b coefficients. The only symbols that have an effect on a number is the symbol BEFORE the number. Thus, in 2b-r, they would separate into 2b and -r.
Using this knowledge, combine like terms the right way.
8b+2b=10b
-4r-r=-5r
The correct equation is 10b-5r
Hope this helps!