в) {3(x+y)+1=x+4y, 7-2(x-y)=x-8y}

1. Simplify the equations: 3x + 3y + 1 = x + 4y => 2x - y = -1. And 7 - 2x + 2y = x - 8y => -3x + 10y = -7.
2. Multiply the first simplified equation by 10: 20x - 10y = -10. Add this to the second simplified equation: (20x - 10y) + (-3x + 10y) = -10 + (-7) => 17x = -17 => x = -1.
3. Substitute x=-1 into 2x - y = -1: 2(-1) - y = -1 => -2 - y = -1 => y = -1.
Answer: x=-1, y=-1