Answer:
 4 bags
Step-by-step explanation:
The number of required bags can be found by dividing the coverage required by the coverage per bag.
Area
The area of Lisa's garden is given by the formula ...
 A = LW
For the given dimensions, the area is ...
 A = (12 ft)(10 ft) = 120 ft²
Bags
The number of required bags can be found by dividing the area by the area per bag:
 (120 ft²)/(30 ft²/bag) = 4 bags
Lisa will need 4 bags of fertilizer to cover the garden.
__
Additional comment
The multiplication relation corresponding to this division relation is ...
 (bags) × (area/bag) = area
To get the relation we used above, we divided both sides by (area/bag).
