The expression $"\frac{3}{10},\frac{n}{30}"$ means

a $10$ percent discount if paid in full within $3$ days, or the net amount is due in $30$ days.

a $3$ percent discount if paid in full within $10$ days, or the net amount is due in $30$ days.

a $3$ percent discount if paid in full within $3$ days, or the net amount is due in $10$ days.

a $3$ percent discount if paid in full within $30$ days, or the net amount is due in $10$ days.

no discount is available on this order; the net amount is due between $10$ and $30$ days.