Transfer Function RLC
The easiest way is to convert each component into a Z component, and then treat them like resistors and break it down to simple algebra before re-introducing the components...

Lets call the first resistor R1 and the second R2, than call all of them Z underscore component name... The || means use the resistors in parallel equation or 'X*Y/(X+Y)'...

Z_final = Z_R1 + [(Z_R2+Z_L)||Z_C]

Reintroducing the values, you would have

Z_final = R + [(R2+Ls)||(1/Cs)]

Further algebra would give you the simplest answer.