The slope of the line is the velocity, or rate of change, of y with respect to x. In other terms, the slope tells you how much y will change for every change in x by one unit. For example if the slope, which is velocity, is 2. y will increase by two units every time x increases by one unit. Your graph is not pictured nor explained, so I cannot give you the specific context beyond the principle that the slope of a line is a constant velocity or rate of change.
Let the length be l, width w and height h, then
Volume = length x width x height
l = 10cm, w + h = 18cm
V(h) = 10(18 - h)h = 180h - h^2
V(h) = 180h - h^2
I'm so sorry if this is wrong but it might be 24.
