The first step to solve this problem is to compute for the area of the rectangular backyard. The formula in computing the area of a rectangle is:
A = LW
Substituting the given measurement to the formula:
A = 31 (24)
A = 744 square feet
The area of the backyard is 744 square feet.
Since each pack of seed covers 12 square feet, you need to divide this to the total area of the backyard.
Therefore, you need 62 (744 / 12) packs of seed to cover the backyard.