б) { y = 2/5*x - 1, 4x - 10y = 10;

1. Substitute the first equation into the second: 4x - 10(2/5*x - 1) = 10.
2. Simplify: 4x - 4x + 10 = 10, which means 10 = 10.
3. The system has infinitely many solutions.