First, we have to find a. Find two congruent sides.
2a-20.4=a+1.6
Add 20.4 to the other side.
2a= a +22
Subtract a from both sides.
a= 22
Now, plug it into every equation and then add the values all together for the perimeter.
18.5
22+1.6= 23.6
22-3.5= 18.5
I already know the last one will be 23.6 since the parallelogram has 2 sets of equal sides.
18.5(2)+23.6(2)= 84.2
84.2 is the perimeter.
I hope this helps!
~kaikers