What you are asking is the difference of circumference of a circle circumscribing a rectangle of 7.8 x 5.5 and a circle circumscribing a rectangle of 7.3 x 3.5

The bigger circle has a diameter 9.544 cm

The smaller circle has a diameter 8.096 cm

Difference in circumference =pi *(9.544-8.096) = pi (1.448) cm = 3.14 *1.448 =4. 548 cm