Answer
The last weight is $20~N$
Work Step by Step
We can see that the weight of $20~N$ hangs on a pulley with two parts of the red cord pulling up on the pulley. Therefore, the tension in the red cord is $10~N$
The last weight hangs on a pulley with two parts of the red cord pulling up on the pulley. Therefore, the last weight is $20~N$.
