Answer:
90
Step-by-step explanation:
a triangle's angles all add up to 180. take 51 and 39 away from 180 and you get 90
Answer: 90 degrees
Step-by-step explanation:
Theorem:
a+b+c=180 degrees
39 degrees + 51 degrees + x degrees = 180 degrees
39 + 51 = 90
180 - 90 = 90
