Answer:
AC = 12
Explanation:
If BC is parallel to DE then ∠D ≅ ∠B and ∠E ≅ ∠C. Therefore
ΔABC is similar to ΔADE.
The sides of smaller triangle are in proportion with sides of bigger triangle.
Therefore we have the equation:
AC/AE = AB/AD
Substitute the given numbers:
x/x+15 =8/18
18x= 8(x+15)
18x = 8x+120
10x = 120
x = 12
AC=12