Y=f(x)=9x^2+18x axis= vertex= y-intercept = x-intercept=

Alake near the arctic circle is covered by a sheet of ice during the cold winter months. when spring arrives, the ice starts to melt. s(t) models the ice sheet's thickness (in meters) as a function of time tt (in weeks). s(t)=-0.25t+4

When only separate discreet points are graphed it is called?

Which one ? is the answer and how to find this answer