Use a number that's divisible by 2 numbers and 84 works - it's divisible by both 12 and 7. You can k10, k2tog 7 times around, or k5, k2tog 12 times around. The 7 times decs will probably work out to a better shaping. So the first dec round will be k10, k2tog, then knit a round. Next round k9, k2tog all the way around, and knit one round. Keep on knitting 1 less st between decs every other round until you're down to about k3 between them. Then dec on every round until you have done decs with just 1k st between them. Then pull the tail through the remaining sts (should be 14 I think) like a drawstring and weave it in.