-(-2a+13)+(-9-2)-(-7a-3)
-(-2a+13)-9a-2-(-7a-3)
Distribute the negative sign
-(-2a+13)-9a-2+-1(-7a-3)
-(-2a+13)+-9a+-2+-1(-7a)+(-1)(-3)
-(-2a+13)+-9a+-2+7a+3
Distribute
2a+-13+-9a+-2+7a+3
Combine like terms
2a+-13+-9a+-2+7a+3
(2a+-9a+7a)+(-13+-2+3)
=-12
