I can suggest
Sand being poured from a conveyor belt forms a cone with height h and a semi-vertical angle of 60 degrees. Let the volume of the sand is .
Suppose that the sand is being poured at a constant rate of 0.3m^3/min. Find the rate of increase of the base area.
Was given in the problem?
The volume of a cone, of height h and base radius r, is given by . Here, you are told that the "semi-vertical angle" is 60 degrees so using . , and . That is where that formula came from.
To change to a "rate of change" formula, differentiate both sides with respect to t, using the chain rule.
Using the fact that , you can solve that for , as a function of h.
The area of the base is, of course, so .