C-13-Q087mediumsingle_mcq12+22+⋯+n2=n(n+1)(2n+1)61^2+2^2+\dots+n^2 = \dfrac{n(n+1)(2n+1)}{6}12+22+⋯+n2=6n(n+1)(2n+1) এ n=7n=7n=7 হলে মান কত?a120120120b140140140c204204204d230230