Determine the area of the garden by using the following formula for the area of a triangle:
A = b·h/2
where
b: base = 4 ft
h: height = 6 ft
replace the previous values of the parameters into the formula for A:
A = (4 ft)(6 ft)/2
A = 12 ft²
next, take into account that:
1 bag of fertilizer = 3 ft² of garden
then, you have:
number of bags of fertilizer = (12 ft²)/(3 ft²) = 4 bags