Question

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Explanation:

Step1: Identify similar - shaped parallelograms

The two parallelograms are similar.

Step2: Set up proportion

Let the unknown side be $x$. The ratio of corresponding sides of similar parallelograms is equal. So $\frac{12}{6}=\frac{10}{x}$.

Step3: Cross - multiply and solve

$12x = 6\times10$, then $12x=60$, and $x = 5$.

Answer:

5