Ahhh, math, my specialty

. But I don't get your first question. Because you talk about k, x, and y, but then ask about L and T. Is there more to the problem (like any definitions such as "let L = 3" or something like that?

The second question....use the "trial and error method"....my favorite method. Note that x^2 in computer notation is x squared. You know N can't be 0 or 1, because that gives an answer of 1 and 3 respectively. So start multiplying 3 times itself. 3 x 3 = 9 (which is 3^2)....not 81 so keep going. But..remember 3^3 is simply (3^2) x 3. So take the 9 which you already calculated, and multiply by 3. (3^2) x 3 = 3^3 = 27. Not 81, keep going. 3^4 = (3^3) x 3 = 27 x 3 = 81! There is your answer, N = 4.

Hope that helps a lil!