The answer is 68.
Field had shape of rectangle since has difference in length and width. The perimeter of rectangle can be expressed as:
P = 2 × (a + b)
If:
a = 100 m
b = 70 m
Then
P = 2 × (100 m + 70 m)
P = 2 × 170 m
P = 340 m.
If posts are on every 5 m, the number of needed posts is:
340 m ÷ 5 m = 68.
Thus, 68 posts are needed for the fence.
