If △ABC ∼ △DEF such that 2AB = DE and BC = 6 cm, find EF

When two triangles are similar, then the ratios of the lengths of their corresponding sides are equal.
Here, △ABC ∼ △DEF

$\therefore \frac{\mathrm{AB}}{\mathrm{DE}}=\frac{\mathrm{BC}}{\mathrm{EF}}$

$\Rightarrow \frac{\mathrm{AB}}{2 \mathrm{AB}}=\frac{6}{\mathrm{EF}}$

$\Rightarrow \mathrm{EF}=12 \mathrm{~cm}$