The first 15-minute chain pull caused the balloon to rise 50*15=<<50*15=750>>750 feet.

Releasing the chain for 10 minutes caused the balloon to descend 10*10=<<10*10=100>>100 feet.

The second 15-minute chain pull caused the balloon to rise another 50*15=<<50*15=750>>750 feet.

Thus, at the end of the second chain pull, when the balloon was at its highest elevation, the balloon had risen to an elevation of 750-100+750=<<750-100+750=1400>>1400 feet above the earth's surface.

# Answer

1400
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
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?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
1400
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?
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