The way it is written you should simplify to:
a + 5 - 5, which equals a. The parenthesis are not necessary for this problem, but if you follow normal order of operations rules (parens first, then exponents, then multiply/divide, then add/subtract), you would also end up with a for the answer.
If it was written:
-5(a + 5), then that would simplify to -5a - 25