If the area of the semi-circular region is 77 cm², find its perimeter.

Find the perimeter of a semicircular plate of radius 3.85 cm.

A sheet is 11 cm long and 2 cm wide. Circular pieces 0.5 cm in diameter are cut from it to prepare discs. Calculate the number of discs that can be prepared.

Find the radius and area of a circle if its circumference is 18π cm.