Let Hector's height = h
Let Charley's height = c
Before we can compare the two variables h and c, we need to find the value of each variable

Statement 1: Hector is 5 feet 7 inches tall.
h = 5ft 7'; the value of c was not provided and we cannot compare the known value of variables 'h' with an unknown value of variable c.
Hence, statement 1 is NOT SUFFICIENT.

Statement 2: When Hector stands on a 3-inch thick book, he is 1-inch taller than Charley.
h + 3 = c + 1
If we remove the 3-inch book, we will have;
h + 3 - 1 = c
h + 2 = c
Therefore, Charley is taller than Hector by 2 feet. Hence, statement 2 is sufficient.
Since statement 2 alone is sufficient, the correct answer is B.

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