Let the current number of males be $x$ and the current number of females be $y$. From the given information, the total population of the town is:

$x + y = 18,000 \quad \text{(equation 1)}$

After the increases, the number of males becomes $1.2x$ (a 20% increase), and the number of females becomes $1.15y$ (a 15% increase). The total population after the increases is 21,000, so we have:

$1.2x + 1.15y = 21,000 \quad \text{(equation 2)}$

Now, we have a system of two equations:

1. $x + y = 18,000$
2. $1.2x + 1.15y = 21,000$

Solving the system:

From equation 1, we can express $y$ as:

$y = 18,000 - x$

Substitute this into equation 2:

$1.2x + 1.15(18,000 - x) = 21,000$

Simplify:

$1.2x + 1.15(18,000) - 1.15x = 21,000$ $1.2x + 20,700 - 1.15x = 21,000$ $(1.2x - 1.15x) = 21,000 - 20,700$ $0.05x = 300$ $x = \frac{300}{0.05} = 6,000$

So, the number of males is $x = 6,000$.

Now, substitute this back into equation 1 to find $y$:

$6,000 + y = 18,000$ $y = 18,000 - 6,000 = 12,000$

Conclusion:

The current number of males is 6,000, and the current number of females is 12,000. The difference between the number of males and females is:

$\boxed{6,000}$

Would you like further details or have any questions?

Here are 5 questions related to this problem:

1. What would the total population be if only the males increased by 20%?
2. How would the population change if both males and females increased by 10%?
3. What if the population increase was limited to only males increasing by 25%?
4. Can you determine the percentage of the population that are females initially?
5. How would you represent this scenario graphically?

Tip: When solving word problems, always start by translating the conditions into algebraic equations.