Given that:

$$ L=7,\quad h=6,\quad w=5 $$

Thus,

$$ V=L\times w\times h=7\times5\times6=210 \ cubes\quad(white,black) $$

So the number of white cubes is

$$ White \quad cubes=210\times\frac{1}{2} $$

$$ =105\quad cubes $$