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I don't understand how angle CAD and ADB are equal. Can you please explain this part.
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You can easily get ∣ A C ∣ = 2 ∣ A D ∣ cos 3 5 ° . Apply sine rule to △ B A D to obtain ∣ A B ∣ = ∣ A D ∣ × sin ∠ A B D sin ∠ A D B , with ∠ A D B = 6 0 ° + x , ∠ A B D = 5 5 ° − x . Applying sine rule to △ A B C you get ∣ A B ∣ = ∣ A C ∣ × sin 5 5 ° sin 9 5 ° . Comparing the two expressions for ∣ A B ∣ you can get 5 5 ° − x = 3 0 ° .
How do you know that triangle A B C and triangle B C D are isosceles?
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Because ∠ D B C = 2 5 ° ⟹ ∠ B D C = 5 0 ° − 2 5 ° = 2 5 ° .
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∠ A D C = 5 5 ° , ∠ B C A = ∠ B A C = 3 5 ° , ∠ C A D = ∠ A D B = 3 0 ° . Therefore ∠ B D C = ∠ A D C − ∠ A D B = 5 5 ° − 3 0 ° = 2 5 ° ( △ A B C , △ B C D are isosceles triangles).