Jess observed that 60% of the people at a mall on a particular day shopped for clothes. if 2500 people at the mall did not shop for clothes that day, the number of people who shopped for clothes that day was (only put numeric values, no other symbols)

If 60% did not, then 40% did

Set up a proportion.
60%/ 2500 = 40%/x
60% x = 2500 * 40%
x = (40% / 60%) * 2500
x = (0.4 / 0.6) * 2500
x = 1666.667
You have to round this, but which way? I would go down.

You could do this another way. Find 100% first.
60% of x = 2500
x = 2500 / 0.6
x = 4166.666666

That is the total number of people he saw.
Take out the 2500
4166.66666 - 2500 = 1666.6666
You arrive at the same place. Which do you like better?

Answer might be d.i think