The complex number 8 + 21i is representing a vector of coordinates 8 and 21.
a) Magnitud of the force
Then, the magnitud of the force is the module of the complex number = √[8^2 + 21^2] = √[64 + 441] = √505 = 22.47 pounds
b) Direction of the force.
The direction is given by the angle fo the vector with the positive horizontal axis, which you find using trigonometric ratios"
tan(angle) = 21/8 = 2.625 => angle = arctan(2.625) = 69.45 degrees.
