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{{ printedBook.courseTrack.name }} {{ printedBook.name }} To find the value of $x$ in the given diagram, let's start by labeling the vertices of each of the triangles.

Looking at the markings, we can note a couple of key congruence relationships. $AD≅DBAE≅EC $ This means that $D$ and $E$ are the midpoints of $AB$ and $AC,$ respectively. Therefore, $DE$ is a midsegment of $△ABC.$ The Triangle Midsegment Theorem tells us that, if a segment joins the midpoints of two sides of a triangle, then the segment is $half$ as long as the third side. $DE=21 BC $ Finally, we will substitute the given values into this equation to find $m.$$DE=21 BC$

$3m=21 (60)$

MoveRightFacToNumOne$b1 ⋅a=ba $

$3m=260 $

MultEqn$LHS⋅2=RHS⋅2$

$6m=60$

DivEqn$LHS/6=RHS/6$

$m=10$