x = number of round tables and y = number of rectangular tables
Each round table has 6 chairs. Each rectangular table has 10 chairs.
The total number of chairs must be greater than or equal to 185 .
6x + 10y ≥ 185
There must be no more than 15 rectangular tables.
So the number of rectangular tables must be less than or equal to 15 .
y ≤ 15
There must be no fewer than 6 round tables.
So the number of round tables must be greater than or equal to 6 .
x ≥ 6
The number of rectangular tables must be greater than or equal to one-third the number of round tables.
y ≥ \(\frac13\)x
3y ≥ x
x ≤ 3y