The two triangles are similar, so will have a direct scale factor. We can find this by using the given measurements, 10÷8=1.25. So the scale factor from the smaller to the bigger triangle is 1.25. This means that 1.25×(x+6)=AE. We can solve this as we would with a regular linear equation:
1.25(x+6)=2x+6
1.25x+7.5=2x+6
1.5=0.75x
2=x
∴ AE is 2x+6=10