The answer to (1) is (d). The change of latitude is 55 deg 27 min along a meridian of longitude. This comes to 3327 nm, which is 6161.6 km.
Not possible to answer (2) without the full question. Where is the second position?
You're all wrong on (3). You're trying to treat it as a departure question. It is not. The 2 positions are on a meridian and its anti-meridian. Therefore the shortest way is the Great Circle joining them, which is over the North Pole. So you take the co-latitude of 5612N (which is 33 degree 48 min) and the co-latitude of 6400N (which is 26 degrees), add them together to get 59 degrees and 48 min, which is 3588 nm along the arc of a Great Circle track.
I that part of your problem, Seabass, is that you're looking for 'a method'. There isn't any one method. You have to look at each individual case. Some are change of latitude along the same meridian in the same hemisphere, some are change of latitude along the same meridian in opposite hemispheres, some are meridian and anti-meridian, and some are departure problems. If you draw a little sketch of each problem, it all becomes much clearer.