If $39$ candies are to be distributed to A and B in the ratio of $4:9$, how many more candies does B get than A?

Given total candies = $39$
Ratio of distribution $A:B=4:9$

Total number of ratio parts $=4+9=13$ parts.

Value of $1$ ratio part:

$$1\text{ part}=\frac{39}{13}=3\text{ candies}$$

Difference in parts between B and A:

$$\text{Difference}=9-4=5\text{ parts}$$

Number of extra candies B gets:

$$\text{Extra Candies}=5\times 3=15\text{ candies}$$