Made changes to ch04.asciidoc

ch04.asciidoc

@@ -594,8 +594,9 @@ BIP0039 defines the creation of a mnemonic code and seed as a follows:
 
 The mnemonic code represents 128 to 256 bits, which are used to derive a longer (512-bit) seed through the use of the key-stretching function PBKDF2. The resulting seed is used to create a deterministic wallet and all of its derived keys. 
 
-Table 4-6 and Table 4-7 list some examples of mnemonic codes and the seeds they produce.
+Tables pass:[<xref linkend="table_4-6" xrefstyle="select: labelnumber"/>] and pass:[<xref linkend="table_4-7" xrefstyle="select: labelnumber"/>] list some examples of mnemonic codes and the seeds they produce.
 
+[[table_4-6]]
 .128-bit entropy mnemonic code and resulting seed
 |=======
 | entropy input (128 bits) | 0c1e24e5917779d297e14d45f14e1a1a
@@ -604,7 +605,7 @@ Table 4-6 and Table 4-7 list some examples of mnemonic codes and the seeds they
 8a599b44b93187be6ee3ab5fd3ead7dd646341b2cdb8d08d13bf7
 |=======
 
-
+[[table_4-7]]
 .256-bit entropy mnemonic code and resulting seed
 |=======
 | entropy input (256 bits) | 2041546864449caff939d32d574753fe684d3c947c3346713dd8423e74abcf8c