Question

4 people stand at the corners of a square. Fred stands at point (0,0)
Ted at (1,0) Ed at (1,1) and ned at (0,1). they each pull on a rope connected to the center of the square
(0.5,0.5). Fred exerts 11N, Ted exerts 11N, Ed 17N and Ned 15N. what is the net force exerted on the center point and what is the angle from the positive x-axis

Answer 1

Use symettry. If two are pulling from opposite corners, the net force in that direction is zero. If two are pulling from opposite corners with different forces, the net force is the difference.

Answer 2

If you draw this properly you will observe that along the Fred-Ed line you have a resultant of 6N toward Ed. Along the Ted-Ned line you have a resultant of 4N toward Ned.
If you combine the two new vectors graphically, you have a right triangle with the hypotenuse being the resultant. Use the Pythagorean Theorem to get the magnitude. To get the direction, D, use:
D = tan^-1(4/6)+ 45^o
The above angle is measured from the Eastward direction upward (counterclockwise).