In the Venn diagram, `xi = {text(children in a nursery)}`

`B = {text(children who received a book for their birthday)}`

`T = {text(children who received a toy for their birthday)}`

`P = {text(children who received a puzzle for their birthday)}`

`x` children received all three types of present.

`6` children received a toy and a puzzle. `4` children received a book and a toy. `5` children received a book and a puzzle.

`7` children received a puzzle but not a book and not a toy.

There are `40` children in the nursery.

Find `n(BuuP)`.