Official Solution:If \(x\) and \(y\) are positive integers and \(x \gt y\), then what is the value of \(xy^2 + yx^2\)? The question asks to find the value of \(xy^2 + yx^2=xy(y+x)\).
(1) \(xy = 6\).
By plugging \(xy = 6\) into the equation, it becomes:
what is the value of \(xy(y+x) = 6(y+x)\)? Now, since \(x\) and \(y\) are positive integers and \(x > y\), then from \(xy = 6\) it follows that \(x=6\) and \(y=1\) OR \(x=3\) and \(y=2\), thus \(6(y+x)=42\) or \(6(y+x)=30\). Two different values, thus this statement is NOT sufficient.
(2) \(x\) is a prime number.
This statement alone is clearly insufficient.
(1)+(2) Since from (2) we know that \(x\) is a prime number, then from (1) we get that \(x=3=prime\) and \(y=2\), thus \(6(y+x)=42\). Sufficient.
Answer: C