For this case, the first thing we must do is determine the number of tables that 2 people sit.
For this, we use the following rule of three:
50 tables -----------------> 100%
x ----------------------------> 40%
Clearing x we have:

Then, the number of tables that 4 people feel is given by:

We are now looking for the number of chairs:
Table for 2:

Table for 4:

Total seats:

Answer:
there are 160 seats in the restaurant