The cost to rent a school bus is $100.
The cost of admission for each student is $x.
The teacher is allowed in for free.
The total cost of the field trip is the sum of the cost to rent a school bus and the cost of admission for the students: $100 + ($x * number of students).
We are given that the total cost of the field trip is $350, so we can write: $100 + ($x * number of students) = $350.
Subtracting $100 from both sides, we get: $x * number of students = $250.
Dividing both sides by $x, we get: number of students = $250 / $x.
We are given that the number of students is 25, so we can write: 25 = $250 / $x.
Multiplying both sides by $x, we get: $x * 25 = $250.
Dividing both sides by 25, we get: $x = $10.
The value of x is $10.
#### 10
The answer is: 10
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
The class plans to take a field trip to the zoo. The cost to rent a school bus is $100. The cost of admission is $x per student. The teacher is allowed in for free. If the class has a budget of $350, how many students can go on the field trip?
If we know the answer to the above question is 25, what is the value of unknown variable x?

### Answer:
