Answer:
2 bags
Explanations:
First, we need to get the area of the trapezoid. This is expressed as:

a and b are the bases
h is the height of the trapezoid
Given the following parameters
a = 80 feet
b = 120 feet
h = 60 feet
Substitute the given parameters into the formula:

If each bag covers 4000 square feet of the lawn, the number of bags needed to be purchased is expressed as:

This shows that 2 bags of fertilizer must be purchased to cover the lawn (to the nearest bag)