Joe, a carpenter with a weight of 600 N, is working on a scaffold. His young son Jack is helping him. Jack has a weight of 450 N. The scaffold is held up by two ropes. One rope has an upward tension of 750 N. The weight of the scaffold is 400 N. What is the upward tension in the other rope?
a) 550 N
b) 650 N
c) 700 N
d) 800 N