[Middle line of a trapezoid]

The middle line of a trapezoid is 6, and the difference between the bases is 4. Find the bases.

#
Let the bases of the trapezoid be $a$ and $b(a>b)$. By the theorem of the midline of a trapezoid, $\frac{a+b}{2}=6$. From the system

$$
\left\{\begin{array}{l}
a+b=12 \\
a-b=4
\end{array}\right.
$$

we find that $a=8, b=4$.

## Answer

4 X 8.