The area of the deck is 30 feet by 40 feet, which means the total area is 30 * 40 = 1200 square feet.
The cost per square foot is $3, so the cost of the deck without sealant is 1200 * $3 = $3600.
Mark paid an extra $x per square foot for sealant, so the total cost with sealant is $3600 + 1200 * $x.
We are given that the total cost is $4800, so we can write: $3600 + 1200 * $x = $4800.
Simplifying the left side, we get: $3600 + $1200 * $x = $4800.
Subtracting $3600 from both sides, we get: $1200 * $x = $1200.
Dividing both sides by $1200, we get: $x = 1.
The value of x is 1.
#### 1
The answer is: 1
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
Mark constructed a deck that was 30 feet by 40 feet.  It cost $3 per square foot.  He then paid an extra $x per square foot for sealant.  How much did he pay?
If we know the answer to the above question is 4800, what is the value of unknown variable x?

### Answer:
