You first need to convert fee to inches 4 feet times 12 inches is 48 inches
20 feet times 12 inches is 240 inches
Now you can set up the equation by saying that the total number of plants is P
Length of the garden is L
Width of the garden is W
Width and length of each plant is x
P=L/X + W/X
Plug in the values
P=48/8 + 240/8
P=6+30
P=36 plants