The following data relate to the marks of $48$ students in Statistics:$56$ $10$ $58$ $38$ $21$ $43$ $12$ $22$\displaystyle$48$ $51$ $39$ $24$ $17$ $36$ $19$\displaystyle$48$ $36$ $15$ $33$ $30$ $62$ $57$ $17$\displaystyle$5$ $17$ $45$ $46$ $43$ $55$ $57$ $38$\displaystyle$43$ $28$ $32$ $35$ $54$ $27$ $17$ $16$\displaystyle$11$ $43$ $45$ $2$ $16$ $46$ $28$ $45$What are the frequency densities for the class intervals $20-30, 30-40, 40-50, 50-59$?