It can't be done. The smaller top triangle is similar to the large (overall) triangle, but this will only give you ratios, not specific numbers. The best I can say is that:

(3x + 2)/(10x - 4) = (3y - 18)/([3y- 18] + [2(y - 5)])

or

(3x + 2)/(10x - 4) = (3y - 18)/(5y - 28)

-Dan