Answer: 5
Step-by-step explanation:
One method is to count all of the values that are between 15 and 19. Those values are highlighted in the diagram below. There are 5 values marked.
An alternative method is to note there are 19 values total. The items in the given table add to 5+2+1+2+4 = 14, so there must be 19-14 = 5 items missing to completely fill out the table.