(-7x+13)-(6x+15)

Answer 1

Answer:
=−6x−9
( math calculator: mathpapa.com )

Answer 2

with no math calculator, but knowing basic algebra .....
(-7x+13)-(6x+15)
- -7x + 13 - 6x - 15
= -13x - 2

using a good webpage:
https://www.wolframalpha.com/input/?i=simplify+%28-7x%2B13%29-%286x%2B15%29