Two bars, AB and BCE $,$ and the link DF are used to support a $750$ N load. The pin E can slide freely along the slot on link DF as shown in the figure. The horizontal bar BCE has a cross sectional area $A_{\text{B}\text{C}\text{E}}=20m{m}^2$ and pin C has a diameter of $4$ mm $.$ Determine

a$)$ internal forces and moment at section $a-a$ in bar BCE.

b$)$ average normal and shear stresses at section $a-a.$

c$)$ shear stress at pin C if it is under single shear.

d$)$ shear stress at pin C if it is under double shear.