Answer:
Here is the complete question.
Originally 21 acts were tentatively scheduled to perform at the arena; only 10 have been booked. What is the shortfall if the other acts do not perform, assuming an average profit margin of $175,000 for each concert?
The shortfall is of 
Explanation:
If all the acts were performed then the earnings would be 
Now as mentioned in the question that only
have been performed so far.
Now the earning from these
acts 
To find the shortfall.
We have to subtract the expected earnings with the actual earning from the concert.
So shortfall 
So the shortfall is of
if the other acts were not performed.