Total magnification is the magnification of the objective lens multiplied with the magnification of the ocular lens.
The usual ocular lens magnification will either be 8x or 10x depending on the microscope you are using.
The magnification in your question is 40x.
Then it means either multiplying (40x)(8x) or (40x)(10x).
So the total magnification could either be 320x or 400x.
