Answer:
B) Subtraction Property of Equality
Step-by-step explanation:
In step 8, it says 77 degrees + m<C = 90 degrees. Then in step 9, it is simplified to m<C = 13 degrees... but how did we get there? Well, if you subtract 77 from 90, you get 13. So, it would be the subtraction property of equality since we had to subtract 77 on both sides to isolate m<C. Hope that helps, I'm 100% sure on this one :)
