Well, honestly I just pushed the numbers around a bit. There's more than one way to do this but if you divide the total number of sts by the number to decrease (80/10) and then figure that the 10th set of 8 sts should be divided on the front edges of the cardigan so that they look even (5 on one side, 3 on the other), that's it.
5/8/8/8/8/8/8/8/8/8/3 or with the decreases
k3 k2tog (k6,k2tog) 9 times, k3.
Glad it worked for you. Enjoy knitting the sweater!