35. Optical Instruments

A 60-power telescope has an eyepiece with a focal length of 4cm. How long is this telescope?

In order to clearly see the Great Red Spot, a persistent storm visible on the surface of Jupiter, you'd need an angular magnification of no less than 150. If you have a telescope with an objective lens with a focal length of 1800mm, what is the maximum focal length of the eyepiece?