Explain Why the Following Statement Is True $$3 + 6 + 9 + \cdots + 3 n \text { is } O \left( n ^ { 2 } \right)$$

question 4

Essay

Explain why the following statement is true. (You may use the theorem on polynomial orders.) $$3 + 6 + 9 + \cdots + 3 n \text { is } O \left( n ^ { 2 } \right)$$