With n is the number of edges that polygon have , we have this formula to calculate the sum of interior angles :

\(\left(n-2\right).180^0\)

So , apply this formula into the thread , we have : 

The sum of the degree measures of the interior angles of a regular octagon is :

\(\left(8-2\right)\cdot180^0=1080^0\)

The sum of the degree measures of the interior angles of a regular octagon is:

                 180^o(8 - 2) = 1080^o

                                    Answer: 1080^o

The answer is : \(180^0\left(8-2\right)=1080^0\)