What comes next in the following series? a,31,s,30,o,31.n,30,d,31

What are correct trigonometric ratios that could be used to determine the length of ln

For the rule of 78, for a 12-month period, the last term in the sequence is 12 and the series sums to 78. for an 10 month period, the last term is and the series sum is . for a 15 month period, the last term is and the series sum is . for a 20 month period, the last term is and the series sum is

The difference of three and the reciprocal of a number is equal to the quotient of 20 and the number. find the number.