The external dimensions of a closed wooden box are 48 cm, 36 cm, 30 cm.

Given that,

The external dimensions of the wooden box are as follows:

Length (l) = 48 cm, Breadth (b) = 36 cm, Height (h) = 30 cm

Now, the internal dimensions of the wooden box are as follows:

Length (l) = 48 - (2 * 1.5) = 45 cm

Breadth (b) = 36 - (2 * 1.5) = 33 cm

Height (h) = 30 - (2 * 1.5) = 27 cm

Internal volume of the wooden box $=1^{*} \mathrm{~b}^{*} \mathrm{~h} \mathrm{~cm}^{3}$

$=45 * 33 * 27 \mathrm{~cm}^{3}$

$=40095 \mathrm{~cm}^{3}$

Volume of the brick $=6^{*} 3^{*} 0.75=13.5 \mathrm{~cm}^{3}$

Therefore, Number of bricks = 40095/13.5 = 2970 bricks

Therefore, 2970 bricks can be kept inside the wooden box.