(a)Radius (r) of semi-circular part = (2.8/2)cm = 1.4 cm

Perimeter of the given figure = 2.8 cm + πr

= 2.8 cm + (22/7 x 1.4)cm

= 2.8 cm + 4.4 cm = 7.2 cm

(b) Radius (r) of semi-circular part = (2.8/2)cm = 1.4 cm

Perimeter of the given figure = 1.5 cm + 2.8 cm + 1.5 cm +π (1.4 cm)

= 5.8 cm + 22/7(1.4 cm)

= 5.8 cm + 4.4 cm = 10.2 cm

(c) Radius (r) of semi-circular part = (2.8/2)cm = 1.4 cm

Perimeter of the figure(c) = 2 cm + πr + 2 cm

= 4 cm + 22/7 x (1.4 cm)

= 4 cm + 4.4 cm = 8.4 cm

Thus, the ant will have to take a longer round for the food-piece (b), because the perimeter of the figure given in alternative (b) is the greatest among all.