For (a), the only point from A, B, C reachable in only two steps is A. You can also go from O to O by moving a step in one direction and then moving back to O.
You cannot go from O to O or from O to A in three steps (why?). However, you can go to B or C in exactly three steps for both.
For (b), you can get to (1, 0) in one step. It is therefore possible to get to (1, 0) in three steps by including one direction and its opposite (up, down, for instance). Also, you must take into account that each possible combination of moves (up, down, right, for example) can be done in any order, and each possible order is a different journey. Finally, there must always be a move to the right.
For (c), use the same trick you did for (b). Since you can get to (100, 0) in 100 moves, if you use 102 moves you can include one direction and its opposite in addition to 100 moves to the right.