Answer
Step-by-step explanation
Let the original stock market level be x.
At the beginning of the day the stock market goes up 50 1/2 (or 50.points and stays at this level for most of the day
New stock market level = (x + 50.5)
At the end of the day the stock market goes down 90 1/4 (or 90.25) points from the at the beginning of the day.
The stock market level is then = x + 50.50 - 90.25
= x - 39.75