Line Plots · Medium problem

There are $20$ students in a class, and each one is shown by one X on a line plot of how many brothers and sisters they have. Above $1$ there are $4$ X's, above $3$ there are $6$ X's, and above $4$ there are $3$ X's. The only other stack is above $2$, but part of the plot was torn off. How many X's are above $2$?