Answer: There are 8 pepperoni pizzas she order.
Explanation:
Since we have given that
Number of vegetable pizzas and pepperoni pizzas for the eighth grade party = 51
Let the number of pepperoni pizzas be 'p'.
Let the number of vegetable pizzas be 'v'.
According to question,

So, it becomes,

Hence, there are 8 pepperoni pizzas she order.