You should mention the unite after your rectangular field's length.

anyway i am doing the math by assuming the unites as km.

the length of the field is 72km and wide 58km.

so the parameter od the rectangle is 2(length+wide) = 2(72+58)= 2x130= 260km

now its takes 1 hour for the person to cover 3km, them it takes (260/3) hourse to cover 260km.

so the answer is 86 hours (assuming the unites are km).