Answer: $13.39
Step-by-step explanation:
first, you take 25% off 21, by multiplying 21*.25 which is 5.25
next, subtract 5.25 from 21, which gets you 15.75
next, add the 15% off coupon, by multiplying 15.75*.15 which is 2.3625
last, subtract 2.3625 from 15.75, which gets you 13.3875, or $13.39 rounded