When two forces or more act on one object, the net force or the resultant force is found by using the parallelo gram law of forces or vectors. If P & Q are forces, construct a parallelogram with the sides proportional to their magnitudes, and the angle between them equal to the angle Ф betwen the forces.
Then the resultant of the two forces is the diagonal passing the intersection of the two forces.
so the length of the diagonal = resultant force = R
R² = P² + Q² + 2 P Q cos Ф
the angle made by R with P is given by : tan α = Q sin Ф / (P+Q cosФ)
R = 20√3 Newton Ф = 60 deg cos Ф= 1/2
forces are equal P = Q
So (20√3)² = P² + P² + 2 P P 1/2
=> 400 * 3 = 3 P² => P² = 400 So P = 20 newotns