To solve questions of these sorts, bring all the terms to one side & simplify it leaving x alone in the other side of the equation (other side of the equal to sign). After simplification you'll get the value of x.
Remember that the signs & operations will change when you bring a term to the other side of the equation.
So, addition will become subtraction, subtraction will become addition, multiplication will become division & division will become multiplication.
4 tables. 4*4 is 16, meaning that even if 4 players want to sit together it doesn't make a difference. With 16 players and 4 at a table we are going to need 4 tables.