The answer here is 36 N. Find the angles in the triangles, the forces in the strings will be proportional but not equal. Find the vertical component of the tension in the upper cable and then take away the gravitational force acting on the top an it will give you the vertical component of the bottom. Remember that they are similar triangles, so the force acting along the horizontal is the same proportions as the vertical. You can also use trig values at the end of the problem. (Lower vertical force/ because of angle)