Mohan is a carpenter who specialises in making chairs. For every assignment he undertakes, he charges his commision and cost. His commission is fixed and equals $ ₹560$ per assignment while the cost equals $ ₹2n^2$ where, $n$ is the total number of chairs he makes. If for a certain assignment the average cost per chair is not more than $₹68$, then the minimum and maximum possible number of chairs in the assignment are, respectively.
- $13\:\text{and}\:19$
- $13\:\text{and}\:20$
- $14\:\text{and}\:19$
- $14\:\text{and}\:20$