First Step:
Letter Choice (A), 3 + 11 + 19 + 27 + ---- + (8 * 1 - 5) = 1(4 * 1 - 1)
Second Step:
Letter Choice (C), 3 + 11 + 19 + 27 + ---- + (8k - 5) = k(4k - 1)
Third Step:
Letter Choice (D), 3 + 11 + 19 + 27 + ---- + (8k - 5) + [8(k + 1) - 5] = (k +1)[4(k + 1) - 1]
Hope that helps!!!!