Solve the system of equations: {u+v=4, 3u-5v=20}

1. Multiply the first equation by 5: 5(u+v) = 5(4), which gives 5u + 5v = 20.

2. Add this new equation to the second equation: (5u + 5v) + (3u - 5v) = 20 + 20, which simplifies to 8u = 40.

3. Solve for u: u = 40 / 8 = 5.

4. Substitute u=5 into the first equation: 5 + v = 4. Solve for v: v = 4 - 5 = -1.

Answer: u=5, v=-1