3. (5 points) If “*” represents an operation, and satisfies the following relationships:
(1) $1 * 1=1$;
(2) $(n+1) * 1=3 \times(n * 1)$

then $5 * 1-2 * 1=$ $\qquad$
【Solution】When $n=1$, $2 * 1=3 \times(1 * 1)=3 \times 1=3$, when $n=2$, $3 * 1=3 \times(2 * 1)=3 \times 3=9$, when $n=3$, $4 * 1=3 \times(3 * 1)=3 \times 9=27$, when $n=4$, $5 * 1=3 \times(4 * 1)=3 \times 27=81$, $5 * 1-2 * 1=81-3=78$, so the answer is: 78 .