$\"\"$

The slope m of a non vertical line through any two points is given by,

$\"\"$

Substitute $\"\"$ slope formula.

$\"\"$

$\"\"$ (Subtract: 1 – 3 = – 2)

$\"\"$ (Multiply each side by negative 2)

$\"\"$ (Cancel common terms) $\"\"$

$\"\"$ (Subtract 9 from each side)

$\"\"$ (Apply additive inverse property: $\"\"$ )

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

$\"\"$ (Multiply each side by negative one)

$\"\"$ (Product of two same signs is positive) $\"\"$

The value of $\"\"$ .