Let the number of chairs Gavin build per week is x and number of tables he builds per week is y.
It takes 4 hours to work on a chair and 10 hours to work on a table. So time taken to work on x chairs and y tables will be:

Gavin wants to work for no more than 40 hours. So we can write the inequality as:

It takes $10 worth of supplies to build a chair and $15 worth of supplies to build a table. So cost or worth of supplies for x chairs and y tables will be:

Gavin wants to spend no more than $80 on material. So we can write the inequality as:

Thus the system of inequalities is:


We can observe the possible combinations from the graph of these inequalities, which is shown below:
a) 0 chair and 3 tables
b) 5 chairs and 2 tables
c) 8 chairs and 2 tables