This sounds easy and I might be overthinking it..
My instructor wants me to remove a circular concave shape from the top of the rectangle.
Is this as simple as making the rectangle, making a new plane, and doing a cut extrude of circular shape through the existing rectangle?
In SW there are many ways of achieving a result. I think your instructor want to see how you would do it
Change an existing feature?
Remove a feature?
Add a new feature?
And there are many ways to each of those, see how many ways you can do it. Depending on reason for the change may lead to best method. Explore new ways of achieving the same thing.