$\"\"$ $\"\"$ $\"\"$

The expression is $\"\"$ .

$\"\"$ (Remove parentheses)

$\"\"$ (Commutative property: a + b = b + a)

$\"\"$ (Assosiative property: a + (b + c) = (a + b) + c)

$\"\"$ (Distributive property: $\"\"$ ) $\"\"$

$\"\"$ (Additive inverse property: $\"\"$ )

$\"\"$ (Zero product property: $\"\"$ )

$\"\"$ (Add: 3 + 3 = 6) \ \

$\"\"$ (Additive identity property: 6 + 0 = 6) \ \ $\"\"$

The simplified expression is 6.