Solve x and y. 25x + 10y = 20.30

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.