The elephant weighs 3*2000=<<3*2000=6000>>6000 pounds
The donkey weighs 6000*.9=<<6000*.9=5400>>5400 pounds less
So the donkey weighs 6000-5400=<<6000-5400=600>>600 pounds
That means the combined weight is 600+6000=<<600+6000=6600>>6600 pounds
#### 6600