Yes, we have a total of 6 filters in that layer, each of which (as Balaji said) is of shape 5 x 5 x 3. So the total filter shape is 5 x 5 x 3 x 6. The choice of 6 is what Prof Ng calls a “hyperparameter”, meaning a choice that the system designer needs to make. It could have been 4 or 8 or 13, but they decided to make it 6.