It is 9 because you have a 30,60,90 triangle, and then you can use pythagorean theorem.
The answer for number 3 is 3.c
The sequence is incrementing by

Therefore, the sixth number is

Which is 64.
Since she has $6 off for all the pizzas, she can get 10 pizzas with a $6 discount.
She would save $6 since, she has the discount and she would still have something left so she could buy something more if she wished to.