## Algebra: A Combined Approach (4th Edition)

Let $S$ be the number of moons on Saturn. Let $U$ be the number of moons on Uranus. Let $N$ be the number of moons on Neptune. $U=N+13$ $S=2+2N$ $S+U+N=47$ $2+2N+N+13+N=47$ $15+4N=47$ $4N=32$ $N=8$ $U=N+13$ $U=8+13$ $U=21$ $S=2+2N$ $S=2+2(8)$ $S=18$