Lilly bought stock at $83.60. The next day, the priced increased by $15.35. Then this price changed by $-2.15. What was the final stock price?

The stock started off at $83.60 and increased by $15.35, meaning you add that to the original:

$83.60 + $15.35 = $98.95

Then it changed by $-2.15, which means decreased by $2.15:

$98.95 - $2.15 = $96.8

Therefore, the final stock price is $96.8.