Two parallel wires carry currents of 20 A and 40 A in opposite...

Let the first wire carry a current $I_1 = 20 \text{ A}$ in the upward direction and the second wire carry $I_2 = 40 \text{ A}$ in the downward direction.

The third wire is placed midway between them and carries a current $I_3$ antiparallel to $I_1$, which means $I_3$ is in the downward direction.

The magnetic force between two parallel current-carrying wires is attractive if the currents are in the same direction, and repulsive if they are in opposite directions.

The current in the third wire ($I_3$) and the first wire ($I_1$) are in opposite directions. Therefore, the first wire repels the third wire, exerting a force directed away from the $20 \text{ A}$ wire (towards the $40 \text{ A}$ wire).

The current in the third wire ($I_3$) and the second wire ($I_2$) are in the same direction (both downward). Therefore, the second wire attracts the third wire, exerting a force directed towards the $40 \text{ A}$ wire.

Since both individual forces acting on the third wire are directed towards the $40 \text{ A}$ wire, the net magnetic force on it will also be directed towards the $40 \text{ A}$ wire.