See below for a plot of the equation.
The y intercept is the y location where x=0 and can be found by solving 6y=180, which is y=30.
Likewise, the x intercept follows from y=0, so 4x=180 => x=45.
The interpretation of the intercepts is: what is the plan if you go for all small tables (ie., y=0) or all big tables (x=0). The answer is: you can rent either 30 small tables or 45 big ones.
All the other points on the line represent some mix of small and big tables (of course, x and y must be integer because you can't rent half tables).
