Someone me with this geometry question 100% correct only

The depth of a lake at a certain point, wich is a function of the distance of that point from shore, is 30 feet.

The function ƒ is defined by ƒ(x) = (x + 3)(x + 1). the graph of ƒ in the xy-plane is a parabola. which interval contains the x-coordinate of the vertex of the graph of ƒ?

Write an equation for the function that includes the points (2,100)and (3,100)