Answer
In the left diagram, Harry is supported by two ropes that share his weight, so the tension is only 250 N.
The net force on him equals zero.
$$left\, rope + right\, rope - 500 N = 0 $$
In the right diagram, Harry is now supported by only one rope, and if he is to remain in equilibrium, the tension must equal his weight, 500 N.
Since this is above the breaking point of the rope, 300 N, it breaks and Harry gets to take his vacation early.
