The arithmetic series is 7 + 14 + 21 + 28 + .... + 98.

The nth term of an arithmetic sequence is .

Where is first term of the sequence and d is common difference.

Here .

Common difference ,

So d = 7.

The nth term of an arithmetic sequence is .

              (Substitute )

Distribute terms using distributive property: .

                        (Apply additive inverse property: )

                              (Apply additive identity property: )

Apply division property of equality: a = b then .

                         (Divide each side by 7)

                              (Cancel common terms)

n = 14                                 (Divide: )

The sum of an arithmetic series ,

Where is the first term and is the nth term.

             (Substitute )

                 (Add: 7 + 98 = 105)

                       (Multiply: )

                            (Divide: )

The sum of the arithmetic series is 735.