3. (7 points) For $a$ and $b$, define the operation “@” as: $a @ b=(a+5) \times b$. If $x @ 1.3=11.05$, then $x=$
【Solution】Solution: According to the definition: $x @ 1.3=11.05$,
$$
\begin{aligned}
(x+5) 1.3 & =11.05, \\
x+5 & =8.5, \\
x=8.5-5 & =3.5
\end{aligned}
$$

Therefore, the answer is: 3.5