I have length, width, depth of pool and tile width. How could I calculate is it possible to do pool paving without breaking the tiles?
Example: length = 5m, width = 15m, depth = 3m, tile width = 0.1m (tile is square)
Result of this is that it is possible to fill the whole pool without breaking any of the tiles, and for that I would need 19500 tiles. How was that calculated?
You simply add all areas that needs to be covered by tiles. In reality you need a bit of extra space at the sides because the tiles have a certain depth. However, I think this is more a schoolbooks exercise, so we may assume that the tiles have a depth of $0$.
A pool has four sides and one floor, so you need to cover all these five areas:
Short side is $3\times 5$ meter, so we need $30\cdot 50 = 1500$ tiles.
Long side is $3\times 15$ meter, so we need $30 \cdot 150=4500$ tiles.
The floor is $5\times 15$, so we need $50\cdot 150=7500$ tiles.
That would result in $$ 2\cdot 1500 + 2\cdot 4500 + 7500 = 19500 $$ tiles.