Hello!
BC // AB => Thalès
AB/AC = AE/AD = BE/CD
3/(3+8) = AE/(AE+10)
3/11 = AE/(AE+10)
3/11 = AE/(AE+10)
3/11 * (AE+10) = AE/(AE+10) * (AE+10)
(3AE + 30)/11 = AE
(3AE + 30)/11 * 11 = AE * 11
3AE + 30 = 11AE
30 = 11AE - 3AE
30 = 8AE
AE = 30/8
AE = 3.75
AE ≈ 3.8
The answer is AE = 3.8