From the statement, we know that:
• the catering company expect 150 people,
,
• they provide two kinds of tables,
,
• small tables seat 6 people,
,
• large tables seat 10 people.
We define the variables
• x = # of small tables,
,
• y = # of large tables.
From the info above, we see that:
• 6x is the number of people that x small tables can sit,
,
• 10y is the number of people that y large tables can sit.
The sum of 6x and 10y gives us the total number that we can sit and that number must be equal to 150:

a) One possible combination is to choose:
• x = 10,
,
• y = 9.
We verify that the combination sum up 150 people

b) We previously have obtained the equation that represents the relation between x and y, that equation is:

c) If we have the point (20, 5), we have:
• x = 20,
,
• y = 5.
We know that with 6 small tables and 10 larges tables we can sit:

By replacing x = 20 and y = 5 we get:

This result means that we can sit 170 people with (x, y) = (20, 5).
d) The equation that we wrote for this problem is:

If we replace x = 20 and y = 5 we get:

We see that by replacing (x, y) = (20, 5) we obtain different numbers on both sides of the equation. So we conclude that the point (x, y) = (20, 5) is not a solution to the equation.
Answers
a) A possible combination is to have 10 small tables and 9 large tables.
b) The relation between x and y is given by the equation:

c) The point (x, y) = (20, 5) represents the situation where we can sit 170 people.
d) The point (x, y) = (20, 5) is not a solution to the equation.