To determine the number of toppings you chose for your pizza, we can start by setting up the equation using the linear function provided:
\[ f(x) = 0.75x + 9 \]
where:
- \( f(x) \) is the total cost of the pizza,
- \( x \) is the number of toppings,
- The base price of the pizza is $9,
- Each topping costs an additional $0.75.
According to the problem, the total cost (\( f(x) \)) is $13.50. We can set up the equation:
\[ 13.50 = 0.75x + 9 \]
Next, we will solve for \( x \):
- Subtract 9 from both sides:
\[ 13.50 - 9 = 0.75x \]
\[ 4.50 = 0.75x \]
- Divide both sides by 0.75 to isolate \( x \):
\[ x = \frac{4.50}{0.75} \]
- Calculate \( x \):
\[ x = 6 \]
Therefore, you chose to put 6 toppings on your pizza.