Question 1171727
.
<pre>

Let n be the number of sides.


The sum of all exterior angles is 360  degrees.


From the condition, the sum of all interior angles is 3*360 = 1080 degrees.


It gives you an equation


    180*(n-2) = 1080


which implies


    n - 2 = 1080/180 = 6.


Hence,  n = 6 + 2 = 8.


<U>ANSWER</U>.  n = 8  (octagon).
</pre>

Solved.



/\/\/\/\/\/\/


Notice that the assumption that the polygon is regular, &nbsp;is &nbsp;EXCESSIVE &nbsp;and &nbsp;UNNECESSARY: 
I did not use it my solution.


The statement and the solution &nbsp;BOTH &nbsp;are valid for any convex polygon.