Can you me with #20? in details i am so lost

Area of an equilateral triangle is , where s is length of a side; we have s = 2 + 4 + 2 = 8 mm; then area is ;
Area of a semi-circle = (1/2)π, where r is the radius of circle; r = 4/2 = 2 mm; then area is 2π;
The shaded area is - π );