In a rhombus (and in any type of parallelogram), the diagonals intersect in their middle point.
That means the segments AE and EC have the same length.
So we have that:
[tex]\begin{gathered} AE=EC \\ \frac{2}{3}x=x-10 \\ x-\frac{2}{3}x=10 \\ \frac{1}{3}x=10 \\ x=10\cdot3 \\ x=30 \end{gathered}[/tex]
So the value of x is 30.
