Let the income of Bimala $ = 100x $

The income of Amala is $20\%$ more than that of Bimala.

So, the income of Amala $ = 100x \times \frac{120}{100} = 120x $

The ratio of Bimala and Amala $ = 100x : 120x = 5:6 \quad \longrightarrow (1)$

Let the income of Kamala $ = 100y $

The income of Amala $20\%$ less than that of Kamala.

So, the income of Amala $ = 100y \times \frac{80}{100} = 80x $

The ratio fo Kamala and Amala $ = 100y : 80y = 5:4 \quad \longrightarrow (2) $

Now, combining equation $(1)$ and $(2)$, we get

- Bimala : Amala $ = (5 : 6) \times 4 = 20: 24$
- Kamala : Amala $ = (5 : 4) \times 6 = 30: 24$

The ratio of Bimala : Amala : Kamala $ = 20 : 24 : 30 = 10 : 12 : 15 $

If Kamala's income goes down by $4\%$ and Bimala’s goes up by $10\%$. Then,

- Kamala’s income $ = 15 \times \frac{96}{100} = 14 . 4 $
- Bimala’s income $ = 10 \times \frac {110}{100} = 11 $

$\therefore$ The percentage by which kamala’s income would exceed Bimala’s income $ = \frac {(14 . 4 – 11)}{11} \times 100 = \frac {3 .4}{11} \times 100 = 30 . 90 \approx 31.$

Correct Answer$: \text{A}$