The median annual income for the heads of households in a certain city is $44,000. Four such heads of households are randomly selected for inclusion in an opinion poll. Let X be the number (out of four) who have annual incomes below $44,000.

Find the probability distribution.

$\displaystyle \displaystyle\frac{\binom{4}{x}\binom{4}{4-x}}{\binom{y}{4}}, \ \ \ x=0, \ 1, \ 2, \ 3, \ 4$

I don't know what y is.