The perimeter of the garden will be equal to the circumference of the complete circle (two semi-circular parts) plus twice the length of the rectangular part.
Length =20−(72)+(72)=(20−7) m=13 m
Circumference of circle =2πr=2×227×72=22 m
Perimeter of the rectangular part =(13+13) m=26 m
So, perimeter of the garden =(22+26) m=48 m