There are only two outcomes: the set result is a tie-break or it isn't. If p=probability of a tie-break=0.13, then q=1-p=0.87, the probability of no tie-break.
The mean is np where n=260 is the number of sets, so the mean is 0.13×260=33.8.
The variance is npq=260×0.13×0.87=29.406, and the standard deviation is the square root of this=5.42 approx.