The sum of the first four terms of an AP is 28 and sum of the first eight terms

The sum of the first four terms of an AP is 28 and sum of the first eight terms of the same AP is 88. Sum of first 16 terms of the AP is

2) 2,4,6,8,10,12,… is

3) The sum of the first ten terms of an AP is four times the sum of the first five terms, then the ratio of the first term to the common difference is

4) 25 trees are planted in a straight line 5 metres apart from each other. To water them the gardener must bring water for each tree separately from a well 10 metres from the first tree in line with the trees. How far will he move in order to water all the trees beginning with the first if he starts from the well ?

5) Second term of sequence with general term n2 - 4/2 is