For each group of three forces below, determine whether the forces in each pair are pulling at right angles to each other. 13 lb, 35 lb, resultant force 30 lb, no; 20 lb, 15 lb, resultant force 25 lb, yes 13 lb, 35 lb, resultant force 30 lb, yes; 20 lb, 15 lb, resultant force 25 lb, no 13 lb, 35 lb, resultant force 30 lb, no; 20 lb, 15 lb, resultant force 25 lb, no 13 lb, 35 lb, resultant force 30 lb, yes; 20 lb, 15 lb, resultant force 25 lb, yes

From the given problem, I gather that there are only two groups of forces. These are:
13 lb, 35 lb, resultant force 30 lb
20 lb, 15 lb, resultant force 25 lb

We use the pythagorean theorem to determine if the three forces are grouped correctly, such that the resultant force is the hypotenuse.

Resultant Force = √(a² + b²)

So, for the first group,
30 ? √(13² + 35²)
30 ≠ 37.33
Thus, the first group does not pull at right angles to each other.

For the second group,
25 ? √(20² + 15²)
25 = 25
Thus, the second group does pull at right angles to each other.