
This result is actually true for any exterior angle. The exterior angle of a triangle is equal to the sum of the two remote angles, and above is a short proof of it.
Step-by-step explanation:
-7(y-1)= 21
-7y+7=21
-7y=21-7
-7y=14
divide by-7
y=-2
Answer: 
Step-by-step explanation:

Divide by 23

Extract the square root.

There is none except for eleven and that is it