The formula used to find the perimeter is P = 2b + 2s
As in parallelogram length of two opposite sides are equal and other two are equal.
for example in a parallelogram ABCD length of AB is 3cm and AD is 5cm, it means length of AB and CD is equal and AD and BC are equal; so
P = 2(3) + 2(5)
=6 + 10
= 16 cm is the perimeter of parallelogram.