we have magnitude and direction, so we should be thinking vectors here.

draw a diagram showing the Cartesian axis and your vectors.

Let be the vector that represents the force of 120 lbs

and be the vector representing the 200 lbs

then the resultant force is given by:

i suppose you will know how to draw these vectors.

let be the terminal point of

and be the terminal point of

so, we would have

once we have we can figure out what is required of us.

can you continue? do you even know what i am talking about?