Hi there!
First, let's find the proportion of the radius' and set it equal to the proportion of the heights:
12/10 = 30/25
Next, we'll cross multiply. If the numbers are the same, then the solids are similar.
300 = 300
The solids are similar! The scale factor from the larger solid to the smaller solid is 6/5 or 1.2. The scale factor from the smaller solid to the larger solid is 5/6.
Hope this helps!! :)
If there's anything else that I can help you with, please let me know!