What you know just by looking at it is that the triangles are congruent, and y only appears in a side with x, so to find y, you first have to find x.
Because the triangles are congruent, their angles and sides are of equal degrees and length. Therefore you can set them equal to each other and solve. First, lets look at the angle because there is only 1 variable in it and so it is solvable. For the equation 20 = 3x - 8, x = 28/3. The second equation, 1/4x+y = 14.7 (which is found by setting the sides equal to each other), You can plug in 28/3 for x making the equation 28/12+y=14.7. Which makes y = 371/30.