The vertex of the parabola is at (4, -3). When the x-value is 5, the y-value is 6. What is the coefficient of the squared expression in the parabola's equation?
A.2
B.3
C.-3
D.-2

Answer asap and if you do you will get brainliest. catherine buys a gallon of ice cream from the store. after taking it home, she eats a fifth of a gallon of ice cream. her sister eats some of the ice cream as well. if two-thirds of the original amount of ice cream is left, then what fraction of a gallon of ice cream did her sister eat?