For an arithmetic sequence $\left\{ a _ { n } \right\}$ with nonzero common difference, the three terms $a _ { 2 } , a _ { 4 } , a _ { 9 }$ form a geometric sequence with common ratio $r$ in this order. Find the value of $6r$. [4 points]
For an arithmetic sequence $\left\{ a _ { n } \right\}$ with nonzero common difference, the three terms $a _ { 2 } , a _ { 4 } , a _ { 9 }$ form a geometric sequence with common ratio $r$ in this order. Find the value of $6r$. [4 points]