$\"\"$

The sum of an arithmetic series $\"\"$ ,

Where $\"\"$ is the first term and $\"\"$ is the nth term.

The values are $\"\"$ .

$\"\"$

$\"\"$ (Substutite $\"\"$ ) $\"\"$

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

$\"\"$ (Multiply: $\"\"$ )

$\"\"$ (Add: 24 + 4 = 28) \ \

$\"\"$ (Multiply: $\"\"$ $\"\"$ ) $\"\"$

The value of $\"\"$ .