The mole

A student heats a sample of hydrated copper(II) sulfate, $\text{CuSO}_4\cdot x\text{H}_2\text{O}$, in a crucible to constant mass. The results are:

mass of empty crucible = 18.40 g
mass of crucible + hydrated salt = 23.40 g
mass of crucible + anhydrous salt after heating = 21.80 g

What is the value of $x$? ($M_r(\text{CuSO}_4)=160,\ M_r(\text{H}_2\text{O})=18$)