This is how far I have gotten, but am stuck:

P(n):2+4+6+. . . +2n = n(n+1)

P(k):2+4+6+. . . +2k = k(k+1)

P(k+1):2+4+6+. . . +2k+2(k+1) = k(k+1)+(k+1)

That's as far as I know how to get. Am I on the right track? Also, how would I go about solving the problem?