Question

it takes 45 pounds of seeds to completely plant a 5 acre field how many acres can be planted per pound of seed

Answer 1

1/9 acres. It's 9lbs/acre so you dive that by 9 and get 1/9 acres/lbs.

Answer 2

Find the unit rate:

 45 pounds
__________ = 9 acres per pound of seeds 
  5 acres