$\"\"$

The expression is $\"\"$

Subtraction property of equality:

If x + a = b, then x + a - a = b - a, or x = b - a.

$\"\"$ (Subtract 7 from each side)

$\"\"$ (Commutative property: $\"\"$ )

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

$\"\"$ (Subtract: $\"\"$ )

$\"\"$

Check:

Check the solution by substituting $\"\"$ in the original equation.

$\"\"$

$\"\"$ (Add: 7 + 6 = 13)

$\"\"$

The value of $\"\"$ .