Answer: She ordered 4 toppings.
Step-by-step explanation:
Given: Total cost of pizza = $ 12.90
Cost of pizza =$7.50
Price per topping = $1.35
Let x = Number of toppings,
Total cost of pizza = (Cost of pizza) + (price per topping) × (Number of topping)
[tex]12.90= 7.50+1.35x\\\\\Rightarrow\ 1.35x=12.90-7.50\\\\\Rightarrow\ 1.35x=5.4\\\\\Rightarrow\ x=\dfrac{5.4}{1.35}\\\\\Rightarrow\ x=\dfrac{540}{135}=4[/tex]
hence, she ordered 4 toppings.