1, Vì $DE//BC$, theo định lí ta lét:
$\dfrac{AD}{DB}=\dfrac{AE}{EC}=\dfrac{8}{12}=\dfrac{x}{15}$
$\to x=10cm$
2, Ta có: $FI=FH-HI=8,4-6,3=2,1cm$
Vì $IJ//FG$, theo định lí ta lét:
$\dfrac{FI}{FH}=\dfrac{GJ}{GH}=\dfrac{2,1}{8,4}=\dfrac{y}{14}$
$\to y=3,5cm$