biaya pemasangan pagar adalah....

4 x sisi = 84
sisi = 84/4 = 21
radius = 21/2

panjang pagar
(4 x 21/2) +  (1/4 x 2 x pi x 2 x r)
= 42 + (22/7 x 21/2)
= 42 + 33
= 75 m 

biaya:
75 x 100 000
= 7 500 000