Which expression is equivalent to 7(2k)?

1/6k(k + 1)(2k + 1)  

Step-by-step explanation:

(1 / 6) (k + 1) ( [k + 1]  + 1) (2 [k + 1] + 1)  =

(1 /6) ( k + 1) (k + 2) (2k + 3)   =

(1/6) ( k^2 + 3k + 2)(2k + 3)  =

(1 / 6) (2k^3 + 6k^2 + 4k + 3k^2 + 9k + 6)  =

(1 /6) (2k^3 + 9k^2 + 13k + 6)