Hi there!
To figure out the value of x, we'll first need to figure out the length of RT. This is actually very simple! Since we have a 30-60-90 relationship, we know that ST = 2. And since ST = 2, we know that RT = 4. Now that we know that RT = 4, figuring out x is no big deal! Since we have a 45-45-90 relationship, we know that x = 4.
Hope this helps!! :)
If this explanation does not make sense, you'd like more of an explanation with walk-through steps, or need help with another problem, feel free to message me at any time!
Have a great day!