We know that half of the sales are laptops, which means (1/2)*x computers are laptops.
We also know that one-third of the sales are netbooks, which means (1/3)*x computers are netbooks.
The rest of the sales are desktop computers, which means the number of desktop computers is x - [(1/2)*x + (1/3)*x].
Simplifying the expression, we get: x - (3/6)*x - (2/6)*x = x - (5/6)*x = (1/6)*x.
We are given that the number of desktop computers is 12, so we can write: (1/6)*x = 12.
Multiplying both sides by 6, we get: x = 72.
The value of x is 72.
#### 72
The answer is: 72
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
Mr. Lu owns a computer store. For last month, half of their sales are laptops, one-third are netbooks, and the rest are desktop computers. If Mr. Lu's store was able to sell a total of x computers, how many of them are desktop computers?
If we know the answer to the above question is 12, what is the value of unknown variable x?

### Answer:
