In my opinion, this is a very badly worded problem without a conceptually clear picture of what is going on. Knowing the answer, I can back out what the question really was, but let's use the author's confused statement to try and learn something ourselves. First of all, the best answer to the problem as written is zero. That is because the total entropy change (the total change in entropy of the system and its surroundings) for a reversible process is always zero. But what is really being asked is, what is the entropy change for dispersing a given amount of heat into the block of iron. Remember that we are transfering heat from some unspecified hot source, by some unspecified reversible mechanism to the block of iron. To say that the process is reversible means in effect that the maximum amount of work was performed in the process of the heat transfer. The most common example of such a mechanism is the Carnot cycle, which you can read about in your book. Clearly, there must be an equivalent, but opposite entropy change in the heat source. Now the problem is simply to decide what the entropy change is in the cold reservoire of a Carnot cycle. The book states that this is just the heat transferred by a reversible process divided by the temperature of the cold reserviour. Answer: a) 92 J/K, b) 67 J/K