What is the value of x?
$$Statement\ 1:\ x^2+y^2=25$$
$$x^2=25-y^2$$
$$x=\sqrt{25-y^2}\ but\ value\ of\ y\ is\ unknown$$
Hence, we cannot evaluate x. Statement 1 is NOT SUFFICIENT
$$Statement\ 2:\ xy=12$$
$$x=\frac{12}{y}\ but\ value\ of\ y\ is\ unknown$$
Hence, we cannot evaluate x. Statement 2 is NOT SUFFICIENT
Combining both statements together
$$1=>\ x^2+y^2=25\ \ \ \ \ =>x=\sqrt{25-y^2}$$
$$2=>\ xy=12\ \ =>\ x=\frac{12}{y}$$
None of the statement provides the value of y. Hence, we cannot evaluate x.

Therefore, both statements together are NOT SUFFICIENT.

Answer = E