If $x$ and $y$ are positive integers with $3^{x} 5^{y}=225$, then $x+y$ equals
(A) 7
(B) 4
(C) 5
(D) 3
(E) 8
Since $15^{2}=225$ and $15=3 \cdot 5$, then $225=15^{2}=(3 \cdot 5)^{2}=3^{2} \cdot 5^{2}$.

Therefore, $x=2$ and $y=2$, so $x+y=4$.

ANSWER: (B)

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