3. (8 points) In the isosceles trapezoid, the length of the upper base is equal to 3, the length of the lower base is equal to 9, and the height is equal to 4. Then, the perimeter of this isosceles trapezoid is $\qquad$
3. (8 points) As shown in the figure, the length of the upper base of the isosceles trapezoid is 3, the length of the lower base is 9, and the height is 4. Therefore, the perimeter of this isosceles trapezoid is 22.

【Solution】Solution: $(9-3) \div 2=3$,
$$
\begin{array}{l}
\sqrt{3^{2}+4^{2}}=\sqrt{9+16}=5, \\
3+9+5+5=22
\end{array}
$$

Answer: The perimeter of this isosceles trapezoid is 22.
Therefore, the answer is: 22.