Question

Find the angle between the forces given the magnitude of their resultant. (Hint: Write force 1 as a vector in the direction of the positive x-axis and force 2 as a vector at an angle θ with the positive x-axis. Round your answer to one decimal place.)
Force 1: 2700 pounds
Force 2:1100 pounds
Resultant Force:3600 pounds

Answer 1

make your sketch, you should end up with a triangle with sides given
(the 3600 is the diagonal of the corresponding parallelogram)

using the cosine law, find the angle opposite the 3600, it should be a large
obtuse angle. Once you have that, use your parallelogram properties to find
the angle between the two forces.

Answer 2

i got 138.7° as final answer. is it correct?

Answer 3

Yes, that is the angle from the cosine law calculation,
but you wanted the angle between the two forces.
Look at your diagram and see that that angle must be 180 - 138.7