7. If the price of an item after a 50% discount differs from the price after a 30% discount by 81 yuan, then the price of this item after an 80% discount is $(\quad$) yuan.


【Analysis】Solution: Let the price be $x$ yuan, then
$$
\begin{array}{c}
0.7 x-0.5 x=81 \\
0.2 x=81 \\
x=405 \\
\text { Apply an 80% discount: } 405 \times 0.8=324 \text { yuan }
\end{array}
$$