The length, breadth, and height of a cuboid are increased by 20%, 25%, and 40% respectively. Find the percentage increase in its volume.

The length, breadth, and height of a cuboid are increased by $x\%$, $y\%$, and $z\%$ respectively. The percentage increase in volume can be calculated using the formula:

$$\text{Percentage increase} = \left(x + y + z + \frac{xy + yz + zx}{100} + \frac{xyz}{10000}\right)\%$$

Given increases are:
$x = 20\%$
$y = 25\%$
$z = 40\%$

$$\frac{(20 \times 25) + (25 \times 40) + (40 \times 20)}{100}$$ $$= \frac{500 + 1000 + 800}{100}$$ $$= \frac{2300}{100} = 23$$

$$\frac{20 \times 25 \times 40}{10000}$$ $$= \frac{500 \times 40}{10000}$$ $$= \frac{20000}{10000} = 2$$

$$\text{Percentage increase} = 85 + 23 + 2 = 110\%$$

The percentage increase in the volume of the cuboid is 110%. This matches option a.

The final answer is $\boxed{\text{a. 110\%}}$.