Answer:
D
Explanation:
Remark
The first thing you must do is notice that <D = <BEA. Mark it that way on your diagram.
The Second thing you need to notice is that <BEA and <A are equal because <A and <D are marked as equal.
So both the large triangle and the small one are isosceles. because 2 of the 3 angles are equal.
Now are you ready for this? That means that BA = 10 because BA is opposite one of the 2 equal angles in the small triangle. So now you are ready to set up a proportion.
Proportion
AB / AC = AE/AD
Givens
AB = 10
AC = 18
AE = 8
AD = x + 8
Solution
Substitute the Givens into the Proportion.
10/18 = 8/(x + 8) Cross multiply
10(x + 8) = 8 * 18 Simplify both sides
10x + 80 = 144 Subtract 80 from both sides
10x + 80 - 80 = 144 - 80
10x = 64 Divide by 10
10x/10 = 64/10
Answer: x = 6.4