a) {x=y-3, 2y-x=6}

1. Substitute the first equation into the second: 2y - (y-3) = 6.
2. Simplify and solve for y: 2y - y + 3 = 6 => y = 3.
3. Substitute y=3 back into the first equation to find x: x = 3 - 3 => x = 0.
Answer: x=0, y=3