John builds a model rocket that can travel 500 ft in the air.  He builds a second rocket that can travel twice as high.  What is the combined height of the two rockets?
How high does the second rocket go? ** The second rocket goes 500*2=<<500*2=1000>>1000 feet
What is the combined height of the two rockets? ** So the total height is 500+1000=<<500+1000=1500>>1500 feet
#### 1500