Given that the vertices of polygon i.e. quadrilateral #ABDC# are #A(5, 0)#, #B(2, 4)#, #D(-6, 4)# & #C(-3, 0)#.
The area #\Delta_1# of #\Delta BCD# with vertices at #B(2, 4)#, #C(-3, 0)# & #D(-6, 4)# is given as
#\Delta_1=1/2|2(0-4)-3(4-4)-6(4-0)|=16#
Similarly, the area #\Delta_2# of #\Delta ABC# with vertices at #A(5, 0)#, #B(2, 4)# & #C(-3, 0)# is given as
#\Delta_2=1/2|5(4-0)+2(0-0)-3(0-4)|=16#
hence, the area of quadrilateral #ABDC# is the sum of areas of above two triangles given as
#=\Delta_1+\Delta_2#
#=16+16#
#32#
Now, the lengths of all four sides are computed by using distance formula as follows
#AB=\sqrt{(5-2)^2+(0-4)^2}=5#
#AC=\sqrt{(5+3)^2+(0-0)^2}=8#
#CD=\sqrt{(-3+6)^2+(0-4)^2}=5#
#BD=\sqrt{(2+6)^2+(4-4)^2}=8#
hence, the perimeter of the quadrilateral ABCD
#=AB+AC+CD+BD#
#=5+8+5+8#
#=26#