A glance at the schematic should allow you to immediately write:

\$\frac {V_O}{V_{IN}} = \frac{R_2||(R_3+R_4)}{R_1+R_2||(R_3|R_4}\cdot\frac{R_4}{R_3+R_4}\$

which is easily simplified to

\$\frac {V_O}{V_{IN}} = \frac{R_2 R_4}{R_1(R_2+R_3+R_4) + R_2 (R_3+R_4)}\$

A glance at the schematic should allow you to immediately write:

\$\frac {V_O}{V_{IN}} = \frac{R_2||(R_3+R_4)}{R_1+R_2||(R_3|R_4)}\cdot\frac{R_4}{R_3+R_4}\$

which is easily simplified to the following:

\$\frac {V_O}{V_{IN}} = \frac{R_2 R_4}{R_1(R_2+R_3+R_4) + R_2 (R_3+R_4)}\$