So, this is a question from the topic Permutation and Combination.

So basically you have digits 2, 2, 3, 3. Now, using these, you wish to know the number of four digit numbers which can be formed.

No. of 4 digit Numbers = 4!/(2!2!) which is equal to 6.

And these 6 numbers are as follows:

2233

3322

2323

3232

3223

2332

Hope this helps.