Hi Charlie. You need to divide the area by converting both to the same units. Square feet is a good unit to use.

One acre is equal to 43 560 square feet. One lot that is 2 feet by 3 feet is equal to 6 square feet.

So a quick approximation to the answer is: how many times does 6 go into 43 560? This will give the correct answer if there is no "wastage".

You said you have a "square acre". If you mean the area is a square then each side is of length $\sqrt{43560} = 208.7$ feet. How many 2 foot lots can you fit along one side? How many 3 foot lots can you fit along the other side? How many lots does that give you?

Hope this helps,
Stephen La Rocque and Penny Nom