Getting to Bougival

Does the hotel offer any advice?
Three possibilities by public transport, each with 2 connections:

• RER line B into Chatelet les Halles station in Paris, where you change to RER A as far as Gare de Nanterre Préfecture, then Bus 259 departing across the street from there at Esplanade Charles de Gualle to Bougival.

• RER line B into Chatelet les Halles, then RER A to La Grande Arche de La Defense, then tunnel to station La Defense and RER L to Bougival.

• RER B just as far as Paris Gare du Nord, then connect over to Gare St Lazare (by RER E or bus or taxi), then RER L train to Bougival. (On this recent thread PharmerPhil also suggests taking the RoissyBus into the city when your destination there is Gare St Lazare.)

See public transport maps and detailed schedules from RATP.

Taxis from CDG into central Paris have a fixed rate of 50 euros (for instance to Gare St. Lazare), but that won't apply to the suburbs, so expect to pay more if taking a taxi directly to your hotel. Uber does also exist and may be cheaper.

It is a minor point but Ligne L is part of the Transilien network. I only mention that in case the OP looks up the RER system and does not see a reference to Ligne L or is looking for signs that say RER L.