Question

What is the measure of an interior angle of a regular three-sided polygon?

Answer 1

The formula to find the measure of an interior angle is $(n - 2) * 180/n$, where $n$ represents the number of sides in the polygon. In this problem, $n$ would represent $3$. 

Let's plug in the value for $n$
$(3 - 2) * 180/3$
Let's simplify that. 
$=60$

Now we know that the measure of an interior angle of a regular three-sided polygon is 60°. Your answer would be B!

Let me know if you have any questions regarding this problem!
Thanks!
-TetraFish

Answer 2

All the sides are the same and we know that all triangles have to add up to be 180. If all the the sides are equal then the answer is 60.
180/3=60