The total area of the garden is (9 ft)(48 ft), or 432 sq ft.
First I determine how many times 1.5 ft divides into 48 ft: 48/1.5 = 32
Next I determine how many times 1.5 ft divides into 9 ft: 9/1.5 = 6
Imagine the garden divided into 32 * 6 squares of side 1.5 ft:
There are 192 such squares.
That's all we can say, at least until you share how many seeds go into each of these 192 squares.