Networking layers and services

a$)$ Consider the OSI and TCP$/$IP reference models for network communications. Describe how the different layers in these two models map to each other?

b$)$ What is protocol encapsulation and what are some key steps involved?

c$)$ In a hypothetical networking protocol stack, Layer $2$ sends data to a lower Layer $1.$ Layer $2$ has a fixed packet size of $400$ bytes, and Layer $1$ has a fixed packet size of $120$ bytes which includes a $20$ byte header $($i$.$e$.,100$ bytes of data payload$).$ How many Layer $1$ packets are required to send a $16,000$ byte file from Layer $2?$ How many total bytes are sent at Layer $1?$