We want to find the value of $X$ in the given situation.
We are told that the addresses on the south side of the street form an arithmetic sequence, as do the addresses on the north side of the street.
On the south side, the addresses are 4, 10, X, etc., and on the north side they are 3, 9, 15, etc.
To find the value of $X$, we can determine the common difference of the arithmetic sequence.
For the south side, the common difference is the difference between any two consecutive terms. In this case, the common difference is 10 - 4 = 6.
For the north side, the common difference is also 6 since it follows the same pattern as the south side.
Now, we can determine the value of $X$ by adding the common difference to the previous term, which is 10:
$X = 10 + 6 = 16$
Given that the value of $X$ is 16, we can calculate the total number of digits painted on the houses.
On the south side, there are 20 houses, and each house number has two digits. So, the total number of digits on the south side is 20 * 2 = 40.
On the north side, there are also 20 houses, and each house number has two digits. So, the total number of digits on the north side is also 20 * 2 = 40.
Therefore, the total number of digits painted on all the houses is 40 + 40 = 80.
Since the painter charges $\$1$ per digit, the total amount collected is $\$1 * 80 = \$80$.
Therefore, the value of X is 16.
The answer is: 16
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
A street has 20 houses on each side, for a total of 40 houses. The addresses on the south side of the street form an arithmetic sequence, as do the addresses on the north side of the street. On the south side, the addresses are 4, 10, X, etc., and on the north side they are 3, 9, 15, etc. A sign painter paints house numbers on a house for $\$1$ per digit. If he paints the appropriate house number once on each of these 40 houses, how many dollars does he collect?
If we know the answer to the above question is 84, what is the value of unknown variable X?

### Answer:
