So if the shapes are similar, they have to have a number multiple from to get the other triangle. If you divide 63 by 42, you get 1.5. Then you have to divide 54 by 1.5 to get G and that would be 36.
1/2^3=1/8
we have 30 of them so
30.1/8=30/8 => 3 and 6/8 or 3 and 3/4 if simplified
Well plug 0 in for x and solve for y and that is the vertex of your expression