7. In the figure below, there are three scales. By observing the first two scales, we can find that 5 " $\boldsymbol{\Delta}$ " and 3 " $\bigcirc$ " weigh the same, and 1 " " weighs the same as 1 " $\boldsymbol{\Delta}$ " plus 2 " $\boldsymbol{\square}$ ". Therefore, 1 " $\boldsymbol{\Delta}$ " plus 1 " 0 " weighs the same as $\qquad$ " $\square$ ".

保留源文本的换行和格式，直接输出翻译结果如下：

7. In the figure below, there are three scales. By observing the first two scales, we can find that 5 " $\boldsymbol{\Delta}$ " and 3 " $\bigcirc$ " weigh the same, and 1 " " weighs the same as 1 " $\boldsymbol{\Delta}$ " plus 2 " $\boldsymbol{\square}$ ". Therefore, 1 " $\boldsymbol{\Delta}$ " plus 1 " 0 " weighs the same as $\qquad$ " $\square$ ".
Analysis: [Equivalent Substitution] From the problem, we know: $5 \boldsymbol{\Delta}=3 \boldsymbol{\bullet}, 1 \boldsymbol{=}=1 \boldsymbol{\Delta}+2 \boldsymbol{\square}$. Combining the two equations, we get $5 \boldsymbol{\Delta}=3 \boldsymbol{\Delta}+6 \boldsymbol{\square}$, which simplifies to $2 \boldsymbol{\Delta}=6 \boldsymbol{\square}, 1 \boldsymbol{\Delta}=3 \square$.