Below is an instruction that describes a task. Write a response that appropriately completes the request in English. Please answer in English.

### Instruction:
Jo-Bob hopped into the hot air balloon, released the anchor rope, and pulled on the lift chain, which ignited the flame and provided the warm air that caused the balloon to rise.  When the lift chain was pulled, the balloon would rise at a rate of 50 feet per minute.  But when the chain was not being pulled, the balloon would slowly descend at a rate of 10 feet per minute.  During his balloon ride, he pulled the chain for 15 minutes, then released the rope for 10 minutes, then pulled the chain for another 15 minutes, and finally released the chain and allowed the balloon to slowly descend back to the earth.  During his balloon ride, what was the highest elevation reached by the balloon?

### Response:
During the first 15-minute chain-pulling, the balloon rose 50*15=<<50*15=750>>750 feet.
Then, during the 10 minute rope-release, the balloon descended 10*10=<<10*10=100>>100 feet.
Then, during the second 15-minute chain-pulling, the balloon rose another 50*15=<<50*15=750>>750 feet.
Thus, at the end of the second chain pull, the balloon had reached an elevation of 750-100+750=<<750-100+750=1400>>1400 feet above the earth's surface.
Therefore, the highest elevation reached by the balloon was 1400 feet.
#### 1400