1.92 as a percentage of 1.60​

Write an explicit formula that represents the sequence defined by the following recursive formula:

What is the approximate total length of iron edging needed to create the square frame and the two diagonals?

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