Can someone answer these and possibly explain them? Quadratic properties.

If x=-3 is the only x-intercept of the graph of a quadratic equation, which statement best discribes the discriminant of the equation?

Subscriptions to a popular fashion magazine have gone down by a consistent percentage each year and can be modeled by the function y = 42,000(0.96)t. what does the value 42,000 represent in the function?

What unit of been sure would be appropriate for the volume of a sphere with a radius of 2 meters