According to the similarity of triangles we can conclude that two triangles are similar if
[tex]A=K\cdot B[/tex]in which A is the measure of one side of the initial triangle, B is the corresponding side into the other triangle amd k is the scale factor.
Using this
[tex]\begin{gathered} AB=k\cdot(DE) \\ 6=k\cdot21 \\ k=\frac{6}{21} \\ k=\frac{2}{7} \end{gathered}[/tex]using k find the values of x and y
[tex]\begin{gathered} AC=k\cdot DC \\ x=(\frac{2}{7})\cdot(28) \\ x=2\cdot4 \\ x=8 \end{gathered}[/tex][tex]\begin{gathered} BC=k\cdot EC \\ 10=\frac{2}{7}\cdot y \\ y=10\cdot\frac{7}{2} \\ y=35 \end{gathered}[/tex]