Write the Word or Phrase That Best Completes Each Statement $$5 + 10 + 15 + \ldots + 5 n = \frac { 5 n ( n + 1 ) } { 2 }$$

Write the word or phrase that best completes each statement or answers the question.
Use mathematical induction to prove the following statement for all positive integers n.
- $$5 + 10 + 15 + \ldots + 5 n = \frac { 5 n ( n + 1 ) } { 2 }$$