Hi there!
To see if they are similar, we'll first create a proportion: 12/10 = 18/15. Then, we'll cross-multiply. If the result is the same, then they are similar. If not, then the triangles are not similar: 180 = 180. The triangles are similar, so we can write a similarity statement: Triangle UVW ~ Triangle RST. Then, we can simplify 10/12 to find the scale factor, which is 5/6. Therefore, the answer is option 2.
Hope this helps!! :)
If there's anything else that I can help you with, please let me know!