John has a donkey and an elephant.  The elephant weighs 3 tons (a ton is 2000 pounds).  The donkey weighs 90% less.  What is their combined weight in pounds?
The elephant weighs 3*2000=<T>multiply(3, 2000)=6000 pounds
The donkey weighs 6000*.9=<T>multiply(6000, 0.9)=5400.0 pounds less
So the donkey weighs 6000-5400=<T>subtract(6000, 5400)=600 pounds
That means the combined weight is 600+6000=<T>add(600, 6000)=6600 pounds
