Find the sum of n terms of the series 2.4 + 5.6 + 8.8 + 11.10 +---------

Question

$(a)\;2n^2+5n+1\qquad(b)\;(6n^2+n+1)n\qquad(c)\;n(2n^2+5n+1)\qquad(d)\;n^2+2n+1$