Answer:
Your answer should be, B.
Explanation:
So, we can identify this as a transversal, which I will assume you already know what that is. When you have a transversal, you need to follow a certain set of rules, and don't worry, they're very simple.
Angle PSR is a vertical angle of angle OST, which automatically, according to your theorems, postulates, or properties, equal to each other. So with that in mind, you know that STN follows the same rules.
Additionally, where the lines intersect, each corresponding side MUST equal 180 degrees. So to find MTS, all you have to do is 180 minus 73, which gives you 107, completing that line.
Hopefully this isn't confusing!