What is the magnification of the drawing (and how to you calculate it lol)

A student observes and draws an Amoeba, using the high power lens of a microscope. The diameter of the drawing is 100mm. The actual diameter of the Amoeba is 100um. What is the magnification of the drawing?
a) 0.001
b) 100
c) 400
d) 1000

Thanks for the answers :p

Magnification = size in drawing/actual size

Therefore magnification = 100mm/100um

Obviously we need the values in the same units so as 100um = 0.1mm we can deduce

magnification = 100mm/0.1mm = 1000

So the answer is D.