Tire repair for each tire costs x, plus another 50 cents for sales tax.
If Juan needs all 4 tires repaired, the total cost will be 4 * (x + 0.50).
We are given that the final cost is 30, so we can write: 4 * (x + 0.50) = 30.
Simplifying the left side, we get: 4x + 2 = 30.
Subtracting 2 from both sides, we get: 4x = 28.
Dividing both sides by 4, we get: x = 7.
The value of x is 7.
#### 7
The answer is: 7
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
Tire repair for each tire costs x, plus another 50 cents for sales tax. If Juan needs all 4 tires repaired, how much is the final cost?
If we know the answer to the above question is 30, what is the value of unknown variable x?

### Answer:
