If you are using a graphical calculator, then I assume you can find the maximum point and minimum point of the graph by using the "solve" or similar operation on the calculator.

This is when (dy/dx) is equalled to 0, or in your case, when w'(t) = 0. Once you have your maximum and minimum, you can find the range.

Or alternately you can do a bit of calculus and work it out yourself...