We're told that angle A is 20x. The diagram shows we have an equilateral triangle (since all three sides are the same length), so we know that all angles are the same measure and they are equal to 60 degrees.
Equate 20x and 60. So we solve 20x = 60 and that leads to x = 3 after you divide both sides by 20.
Since we have a triangle with all sides equal, we know that AB = AC = 9, therefore y = 9 because y is the length of AB.
