Hello I need help with ques 1. part B. I believe I have my forces mixed up or I am attributing the cos(theta) to the wrong force. Please show steps. Thank you

(33%) Problem 1: Four charges of equal magnitude @ = 75 no are placed on the corners of a O 2 rectangle of sides Dy = 18 cm and Dy = 6 cm as shown in the figure. The charges on the left side of the rectangle are positive while the charges on the right side of the rectangle are negative. For this ....... problem, use the coordinate system and angle & indicated in the figure. D2 ............ -Q 3 to D1 14% Part (a) Which choice best represents a free-body diagram for the charge at the lower left corner of the rectangle? Correct! * 14% Part (b) Enter an equation for the net horizontal force acting on the charge located at the lower left corner of the rectangle in terms of the magnitude of the forces from the three other charges, F1: F2: F3: and the angle 8. Grade Summary Fx = F1 - F2+ F3 cos(0) Deductions 2%