If you meant 25x + 10y =20.30, we can elim. the dec. fraction by mult. all 3 terms by 100:
2500x + 1000y = 2030
Then 1000y = 2030 - 2500x, or y = 2.03 - 2.5x
Without a second equation in x and y, you cannot simplify further, nor can you solve for a specific numerical value for either x or y.