To find the cost per chair, you need to divide the total cost by the number of chairs rented. In this case, the total cost is $150 and the number of chairs is 50.
The correct expression to find the cost per chair is:
\[ \frac{150 \text{ dollars}}{50 \text{ chairs}} \]
So the correct option is:
StartFraction 150 dollars Over 50 chairs EndFraction