Question 244684
This is not an equation since there is no equal sign.
It is an expression.
It can't be solved but can only be reduced or simplified.
(9a-2b)-(5a-3b)
the trick is the minus sign in front of the second set of parentheses.
Did you remember that minus a minus is a plus (+3b)
9a-2b-5a+3b
combine like terms
9a-5a-2b+3b
now simplify
9a-5a=4a
-2b+3b=b
or 
3b-2b=1b=b
so we get
4a+b