If 25% of customers come in after 5:00 pm, then we can expect that 0.25 times the total number of customers come in after 5:00 pm.
Let's use this to find how many customers we expect to come in after 5:00 pm on last Tuesday:
Number of customers who came in after 5:00 pm = 0.25 * 84 = 21
Therefore, we would expect that 21 customers came in after 5:00 pm on last Tuesday.