(i) If a statement is true or false but not both, it is a declarative sentence.

As a result, the expression “15 + 8 > 23” is incorrect.

Because the L.H.S result will always equal the R.H.S result,

As a result, the statement is false.

(ii) If a statement is true or false but not both, it is a declarative sentence.

For some values, y + 9 = 7 will be true, while for others, it will be false.

For example, the preceding phrase is true at y=-2 and false at y=1 or any other value.

As a result, it is not a statement.