The area swept by the small disk is the sum of the areas of a right-angled ring with a radius of 4~5cm and a small circle with the center of the big circle as the center! The part of the right-angle fan must be easy for you to understand, and the latter part needs your reasonable imagination or drawing, because the rolling and sweeping area of a small circle can be simplified as a circle swept by two semicircles on both sides of the diameter and the diameter of the small circle. If you don't understand, I hope you can draw clearly!

s=3. 14*(5^2-4^2)+3. 14* 1^2=3 1.4 cm^2